/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
/* vim: set ft=javascript ts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

"use strict";

/* global XPCNativeWrapper */

// For performance matters, this file should only be loaded in the targeted
// document process. For example, it shouldn't be evaluated in the parent
// process until we try to debug a document living in the parent process.

var { Ci, Cu, Cr } = require("chrome");
var Services = require("Services");
var { XPCOMUtils } = require("resource://gre/modules/XPCOMUtils.jsm");
var promise = require("promise");
var {
  ActorPool, createExtraActors, appendExtraActors, GeneratedLocation
} = require("devtools/server/actors/common");
var { DebuggerServer } = require("devtools/server/main");
var DevToolsUtils = require("devtools/shared/DevToolsUtils");
var { assert } = DevToolsUtils;
var { TabSources } = require("./utils/TabSources");
var makeDebugger = require("./utils/make-debugger");

loader.lazyRequireGetter(this, "ThreadActor", "devtools/server/actors/script", true);
loader.lazyRequireGetter(this, "unwrapDebuggerObjectGlobal", "devtools/server/actors/script", true);
loader.lazyRequireGetter(this, "WorkerActorList", "devtools/server/actors/worker-list", true);
loader.lazyImporter(this, "ExtensionContent", "resource://gre/modules/ExtensionContent.jsm");

// Assumptions on events module:
// events needs to be dispatched synchronously,
// by calling the listeners in the order or registration.
loader.lazyRequireGetter(this, "events", "sdk/event/core");

loader.lazyRequireGetter(this, "StyleSheetActor", "devtools/server/actors/stylesheets", true);

function getWindowID(window) {
  return window.QueryInterface(Ci.nsIInterfaceRequestor)
               .getInterface(Ci.nsIDOMWindowUtils)
               .currentInnerWindowID;
}

function getDocShellChromeEventHandler(docShell) {
  let handler = docShell.chromeEventHandler;
  if (!handler) {
    try {
      // Toplevel xul window's docshell doesn't have chromeEventHandler
      // attribute. The chrome event handler is just the global window object.
      handler = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
                        .getInterface(Ci.nsIDOMWindow);
    } catch (e) {
      // ignore
    }
  }
  return handler;
}

function getChildDocShells(parentDocShell) {
  let docShellsEnum = parentDocShell.getDocShellEnumerator(
    Ci.nsIDocShellTreeItem.typeAll,
    Ci.nsIDocShell.ENUMERATE_FORWARDS
  );

  let docShells = [];
  while (docShellsEnum.hasMoreElements()) {
    let docShell = docShellsEnum.getNext();
    docShell.QueryInterface(Ci.nsIInterfaceRequestor)
            .getInterface(Ci.nsIWebProgress);
    docShells.push(docShell);
  }
  return docShells;
}

exports.getChildDocShells = getChildDocShells;

/**
 * Browser-specific actors.
 */

function getInnerId(window) {
  return window.QueryInterface(Ci.nsIInterfaceRequestor)
               .getInterface(Ci.nsIDOMWindowUtils).currentInnerWindowID;
}

/**
 * Creates a TabActor whose main goal is to manage lifetime and
 * expose the tab actors being registered via DebuggerServer.registerModule.
 * But also track the lifetime of the document being tracked.
 *
 * ### Main requests:
 *
 * `attach`/`detach` requests:
 *  - start/stop document watching:
 *    Starts watching for new documents and emits `tabNavigated` and
 *    `frameUpdate` over RDP.
 *  - retrieve the thread actor:
 *    Instantiates a ThreadActor that can be later attached to in order to
 *    debug JS sources in the document.
 * `switchToFrame`:
 *  Change the targeted document of the whole TabActor, and its child tab actors
 *  to an iframe or back to its original document.
 *
 * Most of the TabActor properties (like `chromeEventHandler` or `docShells`)
 * are meant to be used by the various child tab actors.
 *
 * ### RDP events:
 *
 *  - `tabNavigated`:
 *    Sent when the tab is about to navigate or has just navigated to
 *    a different document.
 *    This event contains the following attributes:
 *     * url (string) The new URI being loaded.
 *     * nativeConsoleAPI (boolean) `false` if the console API of the page has
 *                                          been overridden (e.g. by Firebug),
 *                                  `true`  if the Gecko implementation is used.
 *     * state (string) `start` if we just start requesting the new URL,
 *                      `stop`  if the new URL is done loading.
 *     * isFrameSwitching (boolean) Indicates the event is dispatched when
 *                                  switching the TabActor context to
 *                                  a different frame. When we switch to
 *                                  an iframe, there is no document load.
 *                                  The targeted document is most likely
 *                                  going to be already done loading.
 *     * title (string) The document title being loaded.
 *                      (sent only on state=stop)
 *
 *  - `frameUpdate`:
 *    Sent when there was a change in the child frames contained in the document
 *    or when the tab's context was switched to another frame.
 *    This event can have four different forms depending on the type of change:
 *    * One or many frames are updated:
 *      { frames: [{ id, url, title, parentID }, ...] }
 *    * One frame got destroyed:
 *      { frames: [{ id, destroy: true }]}
 *    * All frames got destroyed:
 *      { destroyAll: true }
 *    * We switched the context of the TabActor to a specific frame:
 *      { selected: #id }
 *
 * ### Internal, non-rdp events:
 * Various events are also dispatched on the TabActor itself that are not
 * related to RDP, so, not sent to the client. They all relate to the documents
 * tracked by the TabActor (its main targeted document, but also any of its
 * iframes).
 *  - will-navigate
 *    This event fires once navigation starts.
 *    All pending user prompts are dealt with,
 *    but it is fired before the first request starts.
 *  - navigate
 *    This event is fired once the document's readyState is "complete".
 *  - window-ready
 *    This event is fired in various distinct scenarios:
 *     * When a new Window object is crafted, equivalent of `DOMWindowCreated`.
 *       It is dispatched before any page script is executed.
 *     * We will have already received a window-ready event for this window
 *       when it was created, but we received a window-destroyed event when
 *       it was frozen into the bfcache, and now the user navigated back to
 *       this page, so it's now live again and we should resume handling it.
 *     * For each existing document, when an `attach` request is received.
 *       At this point scripts in the page will be already loaded.
 *     * When `swapFrameLoaders` is used, such as with moving tabs between
 *       windows or toggling Responsive Design Mode.
 *  - window-destroyed
 *    This event is fired in two cases:
 *     * When the window object is destroyed, i.e. when the related document
 *       is garbage collected. This can happen when the tab is closed or the
 *       iframe is removed from the DOM.
 *       It is equivalent of `inner-window-destroyed` event.
 *     * When the page goes into the bfcache and gets frozen.
 *       The equivalent of `pagehide`.
 *  - changed-toplevel-document
 *    This event fires when we switch the TabActor targeted document
 *    to one of its iframes, or back to its original top document.
 *    It is dispatched between window-destroyed and window-ready.
 *  - stylesheet-added
 *    This event is fired when a StyleSheetActor is created.
 *    It contains the following attribute :
 *     * actor (StyleSheetActor) The created actor.
 *
 * Note that *all* these events are dispatched in the following order
 * when we switch the context of the TabActor to a given iframe:
 *  - will-navigate
 *  - window-destroyed
 *  - changed-toplevel-document
 *  - window-ready
 *  - navigate
 *
 * This class is subclassed by ContentActor and others.
 * Subclasses are expected to implement a getter for the docShell property.
 *
 * @param connection DebuggerServerConnection
 *        The conection to the client.
 */
function TabActor(connection) {
  this.conn = connection;
  this._tabActorPool = null;
  // A map of actor names to actor instances provided by extensions.
  this._extraActors = {};
  this._exited = false;
  this._sources = null;

  // Map of DOM stylesheets to StyleSheetActors
  this._styleSheetActors = new Map();

  this._shouldAddNewGlobalAsDebuggee =
    this._shouldAddNewGlobalAsDebuggee.bind(this);

  this.makeDebugger = makeDebugger.bind(null, {
    findDebuggees: () => {
      return this.windows.concat(this.webextensionsContentScriptGlobals);
    },
    shouldAddNewGlobalAsDebuggee: this._shouldAddNewGlobalAsDebuggee
  });

  // Flag eventually overloaded by sub classes in order to watch new docshells
  // Used by the ChromeActor to list all frames in the Browser Toolbox
  this.listenForNewDocShells = false;

  this.traits = {
    reconfigure: true,
    // Supports frame listing via `listFrames` request and `frameUpdate` events
    // as well as frame switching via `switchToFrame` request
    frames: true,
    // Do not require to send reconfigure request to reset the document state
    // to what it was before using the TabActor
    noTabReconfigureOnClose: true
  };

  this._workerActorList = null;
  this._workerActorPool = null;
  this._onWorkerActorListChanged = this._onWorkerActorListChanged.bind(this);
}

// XXX (bug 710213): TabActor attach/detach/exit/destroy is a
// *complete* mess, needs to be rethought asap.

TabActor.prototype = {
  traits: null,

  // Optional console API listener options (e.g. used by the WebExtensionActor to
  // filter console messages by addonID), set to an empty (no options) object by default.
  consoleAPIListenerOptions: {},

  // Optional TabSources filter function (e.g. used by the WebExtensionActor to filter
  // sources by addonID), allow all sources by default.
  _allowSource() {
    return true;
  },

  get exited() {
    return this._exited;
  },

  get attached() {
    return !!this._attached;
  },

  _tabPool: null,
  get tabActorPool() {
    return this._tabPool;
  },

  _contextPool: null,
  get contextActorPool() {
    return this._contextPool;
  },

  // A constant prefix that will be used to form the actor ID by the server.
  actorPrefix: "tab",

  /**
   * An object on which listen for DOMWindowCreated and pageshow events.
   */
  get chromeEventHandler() {
    return getDocShellChromeEventHandler(this.docShell);
  },

  /**
   * Getter for the nsIMessageManager associated to the tab.
   */
  get messageManager() {
    try {
      return this.docShell
        .QueryInterface(Ci.nsIInterfaceRequestor)
        .getInterface(Ci.nsIContentFrameMessageManager);
    } catch (e) {
      return null;
    }
  },

  /**
   * Getter for the tab's doc shell.
   */
  get docShell() {
    throw new Error(
      "The docShell getter should be implemented by a subclass of TabActor");
  },

  /**
   * Getter for the list of all docshell in this tabActor
   * @return {Array}
   */
  get docShells() {
    return getChildDocShells(this.docShell);
  },

  /**
   * Getter for the tab content's DOM window.
   */
  get window() {
    // On xpcshell, there is no document
    if (this.docShell) {
      return this.docShell
        .QueryInterface(Ci.nsIInterfaceRequestor)
        .getInterface(Ci.nsIDOMWindow);
    }
    return null;
  },

  get outerWindowID() {
    if (this.window) {
      return this.window.QueryInterface(Ci.nsIInterfaceRequestor)
                        .getInterface(Ci.nsIDOMWindowUtils)
                        .outerWindowID;
    }
    return null;
  },

  /**
   * Getter for the WebExtensions ContentScript globals related to the
   * current tab content's DOM window.
   */
  get webextensionsContentScriptGlobals() {
    // Ignore xpcshell runtime which spawn TabActors without a window.
    if (this.window) {
      return ExtensionContent.getContentScriptGlobals(this.window);
    }

    return [];
  },

  /**
   * Getter for the list of all content DOM windows in this tabActor
   * @return {Array}
   */
  get windows() {
    return this.docShells.map(docShell => {
      return docShell.QueryInterface(Ci.nsIInterfaceRequestor)
                     .getInterface(Ci.nsIDOMWindow);
    });
  },

  /**
   * Getter for the original docShell the tabActor got attached to in the first
   * place.
   * Note that your actor should normally *not* rely on this top level docShell
   * if you want it to show information relative to the iframe that's currently
   * being inspected in the toolbox.
   */
  get originalDocShell() {
    if (!this._originalWindow) {
      return this.docShell;
    }

    return this._originalWindow.QueryInterface(Ci.nsIInterfaceRequestor)
                               .getInterface(Ci.nsIWebNavigation)
                               .QueryInterface(Ci.nsIDocShell);
  },

  /**
   * Getter for the original window the tabActor got attached to in the first
   * place.
   * Note that your actor should normally *not* rely on this top level window if
   * you want it to show information relative to the iframe that's currently
   * being inspected in the toolbox.
   */
  get originalWindow() {
    return this._originalWindow || this.window;
  },

  /**
   * Getter for the nsIWebProgress for watching this window.
   */
  get webProgress() {
    return this.docShell
      .QueryInterface(Ci.nsIInterfaceRequestor)
      .getInterface(Ci.nsIWebProgress);
  },

  /**
   * Getter for the nsIWebNavigation for the tab.
   */
  get webNavigation() {
    return this.docShell
      .QueryInterface(Ci.nsIInterfaceRequestor)
      .getInterface(Ci.nsIWebNavigation);
  },

  /**
   * Getter for the tab's document.
   */
  get contentDocument() {
    return this.webNavigation.document;
  },

  /**
   * Getter for the tab title.
   * @return string
   *         Tab title.
   */
  get title() {
    return this.contentDocument.contentTitle;
  },

  /**
   * Getter for the tab URL.
   * @return string
   *         Tab URL.
   */
  get url() {
    if (this.webNavigation.currentURI) {
      return this.webNavigation.currentURI.spec;
    }
    // Abrupt closing of the browser window may leave callbacks without a
    // currentURI.
    return null;
  },

  get sources() {
    if (!this._sources) {
      this._sources = new TabSources(this.threadActor, this._allowSource);
    }
    return this._sources;
  },

  /**
   * This is called by BrowserTabList.getList for existing tab actors prior to
   * calling |form| below.  It can be used to do any async work that may be
   * needed to assemble the form.
   */
  update() {
    return promise.resolve(this);
  },

  form() {
    assert(!this.exited,
               "form() shouldn't be called on exited browser actor.");
    assert(this.actorID,
               "tab should have an actorID.");

    let response = {
      actor: this.actorID
    };

    // We may try to access window while the document is closing, then
    // accessing window throws. Also on xpcshell we are using tabactor even if
    // there is no valid document.
    if (this.docShell && !this.docShell.isBeingDestroyed()) {
      response.title = this.title;
      response.url = this.url;
      response.outerWindowID = this.outerWindowID;
    }

    // Always use the same ActorPool, so existing actor instances
    // (created in createExtraActors) are not lost.
    if (!this._tabActorPool) {
      this._tabActorPool = new ActorPool(this.conn);
      this.conn.addActorPool(this._tabActorPool);
    }

    // Walk over tab actor factories and make sure they are all
    // instantiated and added into the ActorPool. Note that some
    // factories can be added dynamically by extensions.
    this._createExtraActors(DebuggerServer.tabActorFactories,
      this._tabActorPool);

    this._appendExtraActors(response);
    return response;
  },

  /**
   * Called when the actor is removed from the connection.
   */
  destroy() {
    this.exit();
  },

  /**
   * Called by the root actor when the underlying tab is closed.
   */
  exit() {
    if (this.exited) {
      return;
    }

    // Tell the thread actor that the tab is closed, so that it may terminate
    // instead of resuming the debuggee script.
    if (this._attached) {
      this.threadActor._tabClosed = true;
    }

    this._detach();

    Object.defineProperty(this, "docShell", {
      value: null,
      configurable: true
    });

    this._extraActors = null;

    this._exited = true;
  },

  /**
   * Return true if the given global is associated with this tab and should be
   * added as a debuggee, false otherwise.
   */
  _shouldAddNewGlobalAsDebuggee(wrappedGlobal) {
    if (wrappedGlobal.hostAnnotations &&
        wrappedGlobal.hostAnnotations.type == "document" &&
        wrappedGlobal.hostAnnotations.element === this.window) {
      return true;
    }

    let global = unwrapDebuggerObjectGlobal(wrappedGlobal);
    if (!global) {
      return false;
    }

    // Check if the global is a sdk page-mod sandbox.
    let metadata = {};
    let id = "";
    try {
      id = getInnerId(this.window);
      metadata = Cu.getSandboxMetadata(global);
    } catch (e) {
      // ignore
    }
    if (metadata
        && metadata["inner-window-id"]
        && metadata["inner-window-id"] == id) {
      return true;
    }

    return false;
  },

  /* Support for DebuggerServer.addTabActor. */
  _createExtraActors: createExtraActors,
  _appendExtraActors: appendExtraActors,

  /**
   * Does the actual work of attaching to a tab.
   */
  _attach() {
    if (this._attached) {
      return;
    }

    // Create a pool for tab-lifetime actors.
    assert(!this._tabPool, "Shouldn't have a tab pool if we weren't attached.");
    this._tabPool = new ActorPool(this.conn);
    this.conn.addActorPool(this._tabPool);

    // ... and a pool for context-lifetime actors.
    this._pushContext();

    // on xpcshell, there is no document
    if (this.window) {
      this._progressListener = new DebuggerProgressListener(this);

      // Save references to the original document we attached to
      this._originalWindow = this.window;

      // Ensure replying to attach() request first
      // before notifying about new docshells.
      DevToolsUtils.executeSoon(() => this._watchDocshells());
    }

    this._attached = true;
  },

  _watchDocshells() {
    // In child processes, we watch all docshells living in the process.
    if (this.listenForNewDocShells) {
      Services.obs.addObserver(this, "webnavigation-create");
    }
    Services.obs.addObserver(this, "webnavigation-destroy");

    // We watch for all child docshells under the current document,
    this._progressListener.watch(this.docShell);

    // And list all already existing ones.
    this._updateChildDocShells();
  },

  onSwitchToFrame(request) {
    let windowId = request.windowId;
    let win;

    try {
      win = Services.wm.getOuterWindowWithId(windowId);
    } catch (e) {
      // ignore
    }
    if (!win) {
      return { error: "noWindow",
               message: "The related docshell is destroyed or not found" };
    } else if (win == this.window) {
      return {};
    }

    // Reply first before changing the document
    DevToolsUtils.executeSoon(() => this._changeTopLevelDocument(win));

    return {};
  },

  onListFrames(request) {
    let windows = this._docShellsToWindows(this.docShells);
    return { frames: windows };
  },

  onListWorkers(request) {
    if (!this.attached) {
      return { error: "wrongState" };
    }

    if (this._workerActorList === null) {
      this._workerActorList = new WorkerActorList(this.conn, {
        type: Ci.nsIWorkerDebugger.TYPE_DEDICATED,
        window: this.window
      });
    }

    return this._workerActorList.getList().then((actors) => {
      let pool = new ActorPool(this.conn);
      for (let actor of actors) {
        pool.addActor(actor);
      }

      this.conn.removeActorPool(this._workerActorPool);
      this._workerActorPool = pool;
      this.conn.addActorPool(this._workerActorPool);

      this._workerActorList.onListChanged = this._onWorkerActorListChanged;

      return {
        "from": this.actorID,
        "workers": actors.map((actor) => actor.form())
      };
    });
  },

  _onWorkerActorListChanged() {
    this._workerActorList.onListChanged = null;
    this.conn.sendActorEvent(this.actorID, "workerListChanged");
  },

  observe(subject, topic, data) {
    // Ignore any event that comes before/after the tab actor is attached
    // That typically happens during firefox shutdown.
    if (!this.attached) {
      return;
    }
    if (topic == "webnavigation-create") {
      subject.QueryInterface(Ci.nsIDocShell);
      this._onDocShellCreated(subject);
    } else if (topic == "webnavigation-destroy") {
      this._onDocShellDestroy(subject);
    }
  },

  _onDocShellCreated(docShell) {
    // (chrome-)webnavigation-create is fired very early during docshell
    // construction. In new root docshells within child processes, involving
    // TabChild, this event is from within this call:
    //   https://hg.mozilla.org/mozilla-central/annotate/74d7fb43bb44/dom/ipc/TabChild.cpp#l912
    // whereas the chromeEventHandler (and most likely other stuff) is set
    // later:
    //   https://hg.mozilla.org/mozilla-central/annotate/74d7fb43bb44/dom/ipc/TabChild.cpp#l944
    // So wait a tick before watching it:
    DevToolsUtils.executeSoon(() => {
      // Bug 1142752: sometimes, the docshell appears to be immediately
      // destroyed, bailout early to prevent random exceptions.
      if (docShell.isBeingDestroyed()) {
        return;
      }

      // In child processes, we have new root docshells,
      // let's watch them and all their child docshells.
      if (this._isRootDocShell(docShell)) {
        this._progressListener.watch(docShell);
      }
      this._notifyDocShellsUpdate([docShell]);
    });
  },

  _onDocShellDestroy(docShell) {
    let webProgress = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
                              .getInterface(Ci.nsIWebProgress);
    this._notifyDocShellDestroy(webProgress);
  },

  _isRootDocShell(docShell) {
    // Should report as root docshell:
    //  - New top level window's docshells, when using ChromeActor against a
    // process. It allows tracking iframes of the newly opened windows
    // like Browser console or new browser windows.
    //  - MozActivities or window.open frames on B2G, where a new root docshell
    // is spawn in the child process of the app.
    return !docShell.parent;
  },

  // Convert docShell list to windows objects list being sent to the client
  _docShellsToWindows(docshells) {
    return docshells.map(docShell => {
      let webProgress = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
                                .getInterface(Ci.nsIWebProgress);
      let window = webProgress.DOMWindow;
      let id = window.QueryInterface(Ci.nsIInterfaceRequestor)
                     .getInterface(Ci.nsIDOMWindowUtils)
                     .outerWindowID;
      let parentID = undefined;
      // Ignore the parent of the original document on non-e10s firefox,
      // as we get the xul window as parent and don't care about it.
      if (window.parent && window != this._originalWindow) {
        parentID = window.parent
                         .QueryInterface(Ci.nsIInterfaceRequestor)
                         .getInterface(Ci.nsIDOMWindowUtils)
                         .outerWindowID;
      }

      // Collect the addonID from the document origin attributes.
      let addonID = window.document.nodePrincipal.addonId;

      return {
        id,
        parentID,
        addonID,
        url: window.location.href,
        title: window.document.title,
      };
    });
  },

  _notifyDocShellsUpdate(docshells) {
    let windows = this._docShellsToWindows(docshells);

    // Do not send the `frameUpdate` event if the windows array is empty.
    if (windows.length == 0) {
      return;
    }

    this.conn.send({
      from: this.actorID,
      type: "frameUpdate",
      frames: windows
    });
  },

  _updateChildDocShells() {
    this._notifyDocShellsUpdate(this.docShells);
  },

  _notifyDocShellDestroy(webProgress) {
    webProgress = webProgress.QueryInterface(Ci.nsIWebProgress);
    let id = webProgress.DOMWindow
                        .QueryInterface(Ci.nsIInterfaceRequestor)
                        .getInterface(Ci.nsIDOMWindowUtils)
                        .outerWindowID;
    this.conn.send({
      from: this.actorID,
      type: "frameUpdate",
      frames: [{
        id,
        destroy: true
      }]
    });

    // Stop watching this docshell (the unwatch() method will check if we
    // started watching it before).
    webProgress.QueryInterface(Ci.nsIDocShell);
    this._progressListener.unwatch(webProgress);

    if (webProgress.DOMWindow == this._originalWindow) {
      // If the original top level document we connected to is removed,
      // we try to switch to any other top level document
      let rootDocShells = this.docShells
                              .filter(d => {
                                return d != this.docShell &&
                                       this._isRootDocShell(d);
                              });
      if (rootDocShells.length > 0) {
        let newRoot = rootDocShells[0];
        this._originalWindow = newRoot.DOMWindow;
        this._changeTopLevelDocument(this._originalWindow);
      } else {
        // If for some reason (typically during Firefox shutdown), the original
        // document is destroyed, and there is no other top level docshell,
        // we detach the tab actor to unregister all listeners and prevent any
        // exception
        this.exit();
      }
      return;
    }

    // If the currently targeted context is destroyed,
    // and we aren't on the top-level document,
    // we have to switch to the top-level one.
    if (webProgress.DOMWindow == this.window &&
        this.window != this._originalWindow) {
      this._changeTopLevelDocument(this._originalWindow);
    }
  },

  _notifyDocShellDestroyAll() {
    this.conn.send({
      from: this.actorID,
      type: "frameUpdate",
      destroyAll: true
    });
  },

  /**
   * Creates a thread actor and a pool for context-lifetime actors. It then sets
   * up the content window for debugging.
   */
  _pushContext() {
    assert(!this._contextPool, "Can't push multiple contexts");

    this._contextPool = new ActorPool(this.conn);
    this.conn.addActorPool(this._contextPool);

    this.threadActor = new ThreadActor(this, this.window);
    this._contextPool.addActor(this.threadActor);
  },

  /**
   * Exits the current thread actor and removes the context-lifetime actor pool.
   * The content window is no longer being debugged after this call.
   */
  _popContext() {
    assert(!!this._contextPool, "No context to pop.");

    this.conn.removeActorPool(this._contextPool);
    this._contextPool = null;
    this.threadActor.exit();
    this.threadActor = null;
    this._sources = null;
  },

  /**
   * Does the actual work of detaching from a tab.
   *
   * @returns false if the tab wasn't attached or true of detaching succeeds.
   */
  _detach() {
    if (!this.attached) {
      return false;
    }

    // Check for docShell availability, as it can be already gone
    // during Firefox shutdown.
    if (this.docShell) {
      this._progressListener.unwatch(this.docShell);
      this._restoreDocumentSettings();
    }
    if (this._progressListener) {
      this._progressListener.destroy();
      this._progressListener = null;
      this._originalWindow = null;

      // Removes the observers being set in _watchDocShells
      if (this.listenForNewDocShells) {
        Services.obs.removeObserver(this, "webnavigation-create");
      }
      Services.obs.removeObserver(this, "webnavigation-destroy");
    }

    this._popContext();

    // Shut down actors that belong to this tab's pool.
    for (let sheetActor of this._styleSheetActors.values()) {
      this._tabPool.removeActor(sheetActor);
    }
    this._styleSheetActors.clear();
    this.conn.removeActorPool(this._tabPool);
    this._tabPool = null;
    if (this._tabActorPool) {
      this.conn.removeActorPool(this._tabActorPool);
      this._tabActorPool = null;
    }

    // Make sure that no more workerListChanged notifications are sent.
    if (this._workerActorList !== null) {
      this._workerActorList.onListChanged = null;
      this._workerActorList = null;
    }

    if (this._workerActorPool !== null) {
      this.conn.removeActorPool(this._workerActorPool);
      this._workerActorPool = null;
    }

    this._attached = false;

    this.conn.send({ from: this.actorID,
                     type: "tabDetached" });

    return true;
  },

  // Protocol Request Handlers

  onAttach(request) {
    if (this.exited) {
      return { type: "exited" };
    }

    this._attach();

    return {
      type: "tabAttached",
      threadActor: this.threadActor.actorID,
      cacheDisabled: this._getCacheDisabled(),
      javascriptEnabled: this._getJavascriptEnabled(),
      traits: this.traits,
    };
  },

  onDetach(request) {
    if (!this._detach()) {
      return { error: "wrongState" };
    }

    return { type: "detached" };
  },

  /**
   * Bring the tab's window to front.
   */
  onFocus() {
    if (this.window) {
      this.window.focus();
    }
    return {};
  },

  /**
   * Reload the page in this tab.
   */
  onReload(request) {
    let force = request && request.options && request.options.force;
    // Wait a tick so that the response packet can be dispatched before the
    // subsequent navigation event packet.
    Services.tm.dispatchToMainThread(DevToolsUtils.makeInfallible(() => {
      // This won't work while the browser is shutting down and we don't really
      // care.
      if (Services.startup.shuttingDown) {
        return;
      }
      this.webNavigation.reload(force ?
        Ci.nsIWebNavigation.LOAD_FLAGS_BYPASS_CACHE :
        Ci.nsIWebNavigation.LOAD_FLAGS_NONE);
    }, "TabActor.prototype.onReload's delayed body"));
    return {};
  },

  /**
   * Navigate this tab to a new location
   */
  onNavigateTo(request) {
    // Wait a tick so that the response packet can be dispatched before the
    // subsequent navigation event packet.
    Services.tm.dispatchToMainThread(DevToolsUtils.makeInfallible(() => {
      this.window.location = request.url;
    }, "TabActor.prototype.onNavigateTo's delayed body"));
    return {};
  },

  /**
   * Reconfigure options.
   */
  onReconfigure(request) {
    let options = request.options || {};

    if (!this.docShell) {
      // The tab is already closed.
      return {};
    }
    this._toggleDevToolsSettings(options);

    return {};
  },

  /**
   * Handle logic to enable/disable JS/cache/Service Worker testing.
   */
  _toggleDevToolsSettings(options) {
    // Wait a tick so that the response packet can be dispatched before the
    // subsequent navigation event packet.
    let reload = false;

    if (typeof options.javascriptEnabled !== "undefined" &&
        options.javascriptEnabled !== this._getJavascriptEnabled()) {
      this._setJavascriptEnabled(options.javascriptEnabled);
      reload = true;
    }
    if (typeof options.cacheDisabled !== "undefined" &&
        options.cacheDisabled !== this._getCacheDisabled()) {
      this._setCacheDisabled(options.cacheDisabled);
    }
    if ((typeof options.serviceWorkersTestingEnabled !== "undefined") &&
        (options.serviceWorkersTestingEnabled !==
         this._getServiceWorkersTestingEnabled())) {
      this._setServiceWorkersTestingEnabled(
        options.serviceWorkersTestingEnabled
      );
    }

    // Reload if:
    //  - there's an explicit `performReload` flag and it's true
    //  - there's no `performReload` flag, but it makes sense to do so
    let hasExplicitReloadFlag = "performReload" in options;
    if ((hasExplicitReloadFlag && options.performReload) ||
       (!hasExplicitReloadFlag && reload)) {
      this.onReload();
    }
  },

  /**
   * Opposite of the _toggleDevToolsSettings method, that reset document state
   * when closing the toolbox.
   */
  _restoreDocumentSettings() {
    this._restoreJavascript();
    this._setCacheDisabled(false);
    this._setServiceWorkersTestingEnabled(false);
  },

  /**
   * Disable or enable the cache via docShell.
   */
  _setCacheDisabled(disabled) {
    let enable = Ci.nsIRequest.LOAD_NORMAL;
    let disable = Ci.nsIRequest.LOAD_BYPASS_CACHE |
                  Ci.nsIRequest.INHIBIT_CACHING;

    this.docShell.defaultLoadFlags = disabled ? disable : enable;
  },

  /**
   * Disable or enable JS via docShell.
   */
  _wasJavascriptEnabled: null,
  _setJavascriptEnabled(allow) {
    if (this._wasJavascriptEnabled === null) {
      this._wasJavascriptEnabled = this.docShell.allowJavascript;
    }
    this.docShell.allowJavascript = allow;
  },

  /**
   * Restore JS state, before the actor modified it.
   */
  _restoreJavascript() {
    if (this._wasJavascriptEnabled !== null) {
      this._setJavascriptEnabled(this._wasJavascriptEnabled);
      this._wasJavascriptEnabled = null;
    }
  },

  /**
   * Return JS allowed status.
   */
  _getJavascriptEnabled() {
    if (!this.docShell) {
      // The tab is already closed.
      return null;
    }

    return this.docShell.allowJavascript;
  },

  /**
   * Disable or enable the service workers testing features.
   */
  _setServiceWorkersTestingEnabled(enabled) {
    let windowUtils = this.window.QueryInterface(Ci.nsIInterfaceRequestor)
                                 .getInterface(Ci.nsIDOMWindowUtils);
    windowUtils.serviceWorkersTestingEnabled = enabled;
  },

  /**
   * Return cache allowed status.
   */
  _getCacheDisabled() {
    if (!this.docShell) {
      // The tab is already closed.
      return null;
    }

    let disable = Ci.nsIRequest.LOAD_BYPASS_CACHE |
                  Ci.nsIRequest.INHIBIT_CACHING;
    return this.docShell.defaultLoadFlags === disable;
  },

  /**
   * Return service workers testing allowed status.
   */
  _getServiceWorkersTestingEnabled() {
    if (!this.docShell) {
      // The tab is already closed.
      return null;
    }

    let windowUtils = this.window.QueryInterface(Ci.nsIInterfaceRequestor)
                                 .getInterface(Ci.nsIDOMWindowUtils);
    return windowUtils.serviceWorkersTestingEnabled;
  },

  /**
   * Prepare to enter a nested event loop by disabling debuggee events.
   */
  preNest() {
    if (!this.window) {
      // The tab is already closed.
      return;
    }
    let windowUtils = this.window
                          .QueryInterface(Ci.nsIInterfaceRequestor)
                          .getInterface(Ci.nsIDOMWindowUtils);
    windowUtils.suppressEventHandling(true);
    windowUtils.suspendTimeouts();
  },

  /**
   * Prepare to exit a nested event loop by enabling debuggee events.
   */
  postNest(nestData) {
    if (!this.window) {
      // The tab is already closed.
      return;
    }
    let windowUtils = this.window
                          .QueryInterface(Ci.nsIInterfaceRequestor)
                          .getInterface(Ci.nsIDOMWindowUtils);
    windowUtils.resumeTimeouts();
    windowUtils.suppressEventHandling(false);
  },

  _changeTopLevelDocument(window) {
    // Fake a will-navigate on the previous document
    // to let a chance to unregister it
    this._willNavigate(this.window, window.location.href, null, true);

    this._windowDestroyed(this.window, null, true);

    // Immediately change the window as this window, if in process of unload
    // may already be non working on the next cycle and start throwing
    this._setWindow(window);

    DevToolsUtils.executeSoon(() => {
      // Then fake window-ready and navigate on the given document
      this._windowReady(window, true);
      DevToolsUtils.executeSoon(() => {
        this._navigate(window, true);
      });
    });
  },

  _setWindow(window) {
    let docShell = window.QueryInterface(Ci.nsIInterfaceRequestor)
                         .getInterface(Ci.nsIWebNavigation)
                         .QueryInterface(Ci.nsIDocShell);
    // Here is the very important call where we switch the currently
    // targeted context (it will indirectly update this.window and
    // many other attributes defined from docShell).
    Object.defineProperty(this, "docShell", {
      value: docShell,
      enumerable: true,
      configurable: true
    });
    events.emit(this, "changed-toplevel-document");
    this.conn.send({
      from: this.actorID,
      type: "frameUpdate",
      selected: this.outerWindowID
    });
  },

  /**
   * Handle location changes, by clearing the previous debuggees and enabling
   * debugging, which may have been disabled temporarily by the
   * DebuggerProgressListener.
   */
  _windowReady(window, isFrameSwitching = false) {
    let isTopLevel = window == this.window;

    // We just reset iframe list on WillNavigate, so we now list all existing
    // frames when we load a new document in the original window
    if (window == this._originalWindow && !isFrameSwitching) {
      this._updateChildDocShells();
    }

    events.emit(this, "window-ready", {
      window: window,
      isTopLevel: isTopLevel,
      id: getWindowID(window)
    });

    // TODO bug 997119: move that code to ThreadActor by listening to
    // window-ready
    let threadActor = this.threadActor;
    if (isTopLevel && threadActor.state != "detached") {
      this.sources.reset({ sourceMaps: true });
      threadActor.clearDebuggees();
      threadActor.dbg.enabled = true;
      threadActor.maybePauseOnExceptions();
      // Update the global no matter if the debugger is on or off,
      // otherwise the global will be wrong when enabled later.
      threadActor.global = window;
    }

    // Refresh the debuggee list when a new window object appears (top window or
    // iframe).
    if (threadActor.attached) {
      threadActor.dbg.addDebuggees();
    }
  },

  _windowDestroyed(window, id = null, isFrozen = false) {
    events.emit(this, "window-destroyed", {
      window: window,
      isTopLevel: window == this.window,
      id: id || getWindowID(window),
      isFrozen: isFrozen
    });
  },

  /**
   * Start notifying server and client about a new document
   * being loaded in the currently targeted context.
   */
  _willNavigate(window, newURI, request, isFrameSwitching = false) {
    let isTopLevel = window == this.window;
    let reset = false;

    if (window == this._originalWindow && !isFrameSwitching) {
      // Clear the iframe list if the original top-level document changes.
      this._notifyDocShellDestroyAll();

      // If the top level document changes and we are targeting
      // an iframe, we need to reset to the upcoming new top level document.
      // But for this will-navigate event, we will dispatch on the old window.
      // (The inspector codebase expect to receive will-navigate for the
      // currently displayed document in order to cleanup the markup view)
      if (this.window != this._originalWindow) {
        reset = true;
        window = this.window;
        isTopLevel = true;
      }
    }

    // will-navigate event needs to be dispatched synchronously,
    // by calling the listeners in the order or registration.
    // This event fires once navigation starts,
    // (all pending user prompts are dealt with),
    // but before the first request starts.
    events.emit(this, "will-navigate", {
      window: window,
      isTopLevel: isTopLevel,
      newURI: newURI,
      request: request
    });

    // We don't do anything for inner frames in TabActor.
    // (we will only update thread actor on window-ready)
    if (!isTopLevel) {
      return;
    }

    // Proceed normally only if the debuggee is not paused.
    // TODO bug 997119: move that code to ThreadActor by listening to
    // will-navigate
    let threadActor = this.threadActor;
    if (threadActor.state == "paused") {
      this.conn.send(
        threadActor.unsafeSynchronize(Promise.resolve(threadActor.onResume())));
      threadActor.dbg.enabled = false;
    }
    threadActor.disableAllBreakpoints();

    this.conn.send({
      from: this.actorID,
      type: "tabNavigated",
      url: newURI,
      nativeConsoleAPI: true,
      state: "start",
      isFrameSwitching: isFrameSwitching
    });

    if (reset) {
      this._setWindow(this._originalWindow);
    }
  },

  /**
   * Notify server and client about a new document done loading in the current
   * targeted context.
   */
  _navigate(window, isFrameSwitching = false) {
    let isTopLevel = window == this.window;

    // navigate event needs to be dispatched synchronously,
    // by calling the listeners in the order or registration.
    // This event is fired once the document is loaded,
    // after the load event, it's document ready-state is 'complete'.
    events.emit(this, "navigate", {
      window: window,
      isTopLevel: isTopLevel
    });

    // We don't do anything for inner frames in TabActor.
    // (we will only update thread actor on window-ready)
    if (!isTopLevel) {
      return;
    }

    // TODO bug 997119: move that code to ThreadActor by listening to navigate
    let threadActor = this.threadActor;
    if (threadActor.state == "running") {
      threadActor.dbg.enabled = true;
    }

    this.conn.send({
      from: this.actorID,
      type: "tabNavigated",
      url: this.url,
      title: this.title,
      nativeConsoleAPI: this.hasNativeConsoleAPI(this.window),
      state: "stop",
      isFrameSwitching: isFrameSwitching
    });
  },

  /**
   * Tells if the window.console object is native or overwritten by script in
   * the page.
   *
   * @param nsIDOMWindow window
   *        The window object you want to check.
   * @return boolean
   *         True if the window.console object is native, or false otherwise.
   */
  hasNativeConsoleAPI(window) {
    let isNative = false;
    try {
      // We are very explicitly examining the "console" property of
      // the non-Xrayed object here.
      let console = window.wrappedJSObject.console;
      isNative = new XPCNativeWrapper(console).IS_NATIVE_CONSOLE;
    } catch (ex) {
      // ignore
    }
    return isNative;
  },

  /**
   * Create or return the StyleSheetActor for a style sheet. This method
   * is here because the Style Editor and Inspector share style sheet actors.
   *
   * @param DOMStyleSheet styleSheet
   *        The style sheet to create an actor for.
   * @return StyleSheetActor actor
   *         The actor for this style sheet.
   *
   */
  createStyleSheetActor(styleSheet) {
    if (this._styleSheetActors.has(styleSheet)) {
      return this._styleSheetActors.get(styleSheet);
    }
    let actor = new StyleSheetActor(styleSheet, this);
    this._styleSheetActors.set(styleSheet, actor);

    this._tabPool.addActor(actor);
    events.emit(this, "stylesheet-added", actor);

    return actor;
  },

  removeActorByName(name) {
    if (name in this._extraActors) {
      const actor = this._extraActors[name];
      if (this._tabActorPool.has(actor)) {
        this._tabActorPool.removeActor(actor);
      }
      delete this._extraActors[name];
    }
  },

  /**
   * Takes a packet containing a url, line and column and returns
   * the updated url, line and column based on the current source mapping
   * (source mapped files, pretty prints).
   *
   * @param {String} request.url
   * @param {Number} request.line
   * @param {Number?} request.column
   * @return {Promise<Object>}
   */
  onResolveLocation(request) {
    let { url, line } = request;
    let column = request.column || 0;
    const scripts = this.threadActor.dbg.findScripts({ url });

    if (!scripts[0] || !scripts[0].source) {
      return promise.resolve({
        from: this.actorID,
        type: "resolveLocation",
        error: "SOURCE_NOT_FOUND"
      });
    }
    const source = scripts[0].source;
    const generatedActor = this.sources.createNonSourceMappedActor(source);
    let generatedLocation = new GeneratedLocation(
      generatedActor, line, column);
    return this.sources.getOriginalLocation(generatedLocation).then(loc => {
      // If no map found, return this packet
      if (loc.originalLine == null) {
        return {
          type: "resolveLocation",
          error: "MAP_NOT_FOUND"
        };
      }

      loc = loc.toJSON();
      return {
        from: this.actorID,
        url: loc.source.url,
        column: loc.column,
        line: loc.line
      };
    });
  },
};

/**
 * The request types this actor can handle.
 */
TabActor.prototype.requestTypes = {
  "attach": TabActor.prototype.onAttach,
  "detach": TabActor.prototype.onDetach,
  "focus": TabActor.prototype.onFocus,
  "reload": TabActor.prototype.onReload,
  "navigateTo": TabActor.prototype.onNavigateTo,
  "reconfigure": TabActor.prototype.onReconfigure,
  "switchToFrame": TabActor.prototype.onSwitchToFrame,
  "listFrames": TabActor.prototype.onListFrames,
  "listWorkers": TabActor.prototype.onListWorkers,
  "resolveLocation": TabActor.prototype.onResolveLocation
};

exports.TabActor = TabActor;

/**
 * The DebuggerProgressListener object is an nsIWebProgressListener which
 * handles onStateChange events for the inspected browser. If the user tries to
 * navigate away from a paused page, the listener makes sure that the debuggee
 * is resumed before the navigation begins.
 *
 * @param TabActor aTabActor
 *        The tab actor associated with this listener.
 */
function DebuggerProgressListener(tabActor) {
  this._tabActor = tabActor;
  this._onWindowCreated = this.onWindowCreated.bind(this);
  this._onWindowHidden = this.onWindowHidden.bind(this);

  // Watch for windows destroyed (global observer that will need filtering)
  Services.obs.addObserver(this, "inner-window-destroyed");

  // XXX: for now we maintain the list of windows we know about in this instance
  // so that we can discriminate windows we care about when observing
  // inner-window-destroyed events. Bug 1016952 would remove the need for this.
  this._knownWindowIDs = new Map();

  this._watchedDocShells = new WeakSet();
}

DebuggerProgressListener.prototype = {
  QueryInterface: XPCOMUtils.generateQI([
    Ci.nsIWebProgressListener,
    Ci.nsISupportsWeakReference,
    Ci.nsISupports,
  ]),

  destroy() {
    Services.obs.removeObserver(this, "inner-window-destroyed");
    this._knownWindowIDs.clear();
    this._knownWindowIDs = null;
  },

  watch(docShell) {
    // Add the docshell to the watched set. We're actually adding the window,
    // because docShell objects are not wrappercached and would be rejected
    // by the WeakSet.
    let docShellWindow = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
                                 .getInterface(Ci.nsIDOMWindow);
    this._watchedDocShells.add(docShellWindow);

    let webProgress = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
                              .getInterface(Ci.nsIWebProgress);
    webProgress.addProgressListener(this,
                                    Ci.nsIWebProgress.NOTIFY_STATE_WINDOW |
                                    Ci.nsIWebProgress.NOTIFY_STATE_DOCUMENT);

    let handler = getDocShellChromeEventHandler(docShell);
    handler.addEventListener("DOMWindowCreated", this._onWindowCreated, true);
    handler.addEventListener("pageshow", this._onWindowCreated, true);
    handler.addEventListener("pagehide", this._onWindowHidden, true);

    // Dispatch the _windowReady event on the tabActor for pre-existing windows
    for (let win of this._getWindowsInDocShell(docShell)) {
      this._tabActor._windowReady(win);
      this._knownWindowIDs.set(getWindowID(win), win);
    }
  },

  unwatch(docShell) {
    let docShellWindow = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
                                 .getInterface(Ci.nsIDOMWindow);
    if (!this._watchedDocShells.has(docShellWindow)) {
      return;
    }

    let webProgress = docShell.QueryInterface(Ci.nsIInterfaceRequestor)
                              .getInterface(Ci.nsIWebProgress);
    // During process shutdown, the docshell may already be cleaned up and throw
    try {
      webProgress.removeProgressListener(this);
    } catch (e) {
      // ignore
    }

    let handler = getDocShellChromeEventHandler(docShell);
    handler.removeEventListener("DOMWindowCreated",
      this._onWindowCreated, true);
    handler.removeEventListener("pageshow", this._onWindowCreated, true);
    handler.removeEventListener("pagehide", this._onWindowHidden, true);

    for (let win of this._getWindowsInDocShell(docShell)) {
      this._knownWindowIDs.delete(getWindowID(win));
    }
  },

  _getWindowsInDocShell(docShell) {
    return getChildDocShells(docShell).map(d => {
      return d.QueryInterface(Ci.nsIInterfaceRequestor)
              .getInterface(Ci.nsIDOMWindow);
    });
  },

  onWindowCreated: DevToolsUtils.makeInfallible(function (evt) {
    if (!this._tabActor.attached) {
      return;
    }

    // pageshow events for non-persisted pages have already been handled by a
    // prior DOMWindowCreated event. For persisted pages, act as if the window
    // had just been created since it's been unfrozen from bfcache.
    if (evt.type == "pageshow" && !evt.persisted) {
      return;
    }

    let window = evt.target.defaultView;
    this._tabActor._windowReady(window);

    if (evt.type !== "pageshow") {
      this._knownWindowIDs.set(getWindowID(window), window);
    }
  }, "DebuggerProgressListener.prototype.onWindowCreated"),

  onWindowHidden: DevToolsUtils.makeInfallible(function (evt) {
    if (!this._tabActor.attached) {
      return;
    }

    // Only act as if the window has been destroyed if the 'pagehide' event
    // was sent for a persisted window (persisted is set when the page is put
    // and frozen in the bfcache). If the page isn't persisted, the observer's
    // inner-window-destroyed event will handle it.
    if (!evt.persisted) {
      return;
    }

    let window = evt.target.defaultView;
    this._tabActor._windowDestroyed(window, null, true);
  }, "DebuggerProgressListener.prototype.onWindowHidden"),

  observe: DevToolsUtils.makeInfallible(function (subject, topic) {
    if (!this._tabActor.attached) {
      return;
    }

    // Because this observer will be called for all inner-window-destroyed in
    // the application, we need to filter out events for windows we are not
    // watching
    let innerID = subject.QueryInterface(Ci.nsISupportsPRUint64).data;
    let window = this._knownWindowIDs.get(innerID);
    if (window) {
      this._knownWindowIDs.delete(innerID);
      this._tabActor._windowDestroyed(window, innerID);
    }
  }, "DebuggerProgressListener.prototype.observe"),

  onStateChange:
  DevToolsUtils.makeInfallible(function (progress, request, flag, status) {
    if (!this._tabActor.attached) {
      return;
    }

    let isStart = flag & Ci.nsIWebProgressListener.STATE_START;
    let isStop = flag & Ci.nsIWebProgressListener.STATE_STOP;
    let isDocument = flag & Ci.nsIWebProgressListener.STATE_IS_DOCUMENT;
    let isWindow = flag & Ci.nsIWebProgressListener.STATE_IS_WINDOW;

    // Catch any iframe location change
    if (isDocument && isStop) {
      // Watch document stop to ensure having the new iframe url.
      progress.QueryInterface(Ci.nsIDocShell);
      this._tabActor._notifyDocShellsUpdate([progress]);
    }

    let window = progress.DOMWindow;
    if (isDocument && isStart) {
      // One of the earliest events that tells us a new URI
      // is being loaded in this window.
      let newURI = request instanceof Ci.nsIChannel ? request.URI.spec : null;
      this._tabActor._willNavigate(window, newURI, request);
    }
    if (isWindow && isStop) {
      // Don't dispatch "navigate" event just yet when there is a redirect to
      // about:neterror page.
      if (request.status != Cr.NS_OK) {
        // Instead, listen for DOMContentLoaded as about:neterror is loaded
        // with LOAD_BACKGROUND flags and never dispatches load event.
        // That may be the same reason why there is no onStateChange event
        // for about:neterror loads.
        let handler = getDocShellChromeEventHandler(progress);
        let onLoad = evt => {
          // Ignore events from iframes
          if (evt.target == window.document) {
            handler.removeEventListener("DOMContentLoaded", onLoad, true);
            this._tabActor._navigate(window);
          }
        };
        handler.addEventListener("DOMContentLoaded", onLoad, true);
      } else {
        // Somewhat equivalent of load event.
        // (window.document.readyState == complete)
        this._tabActor._navigate(window);
      }
    }
  }, "DebuggerProgressListener.prototype.onStateChange")
};