Bug 1533948, change BrowserTabChild to inherit from JSWindowActor, r=mconley

toolkit/content/widgets/browser-custom-element.js

@@ -599,7 +599,7 @@ class MozBrowser extends MozElements.MozElementMixin(XULFrameElement) {
 
   set characterSet(val) {
     if (this.isRemoteBrowser) {
-      this.messageManager.sendAsyncMessage("UpdateCharacterSet", { value: val });
+      this.sendMessageToActor("UpdateCharacterSet", { value: val }, "BrowserTab");
       this._characterSet = val;
     } else {
       this.docShell.charset = val;
@@ -1860,6 +1860,41 @@ class MozBrowser extends MozElements.MozElementMixin(XULFrameElement) {
       this.docShell.getContentBlockingLog() :
       Promise.reject("docshell isn't available");
   }
+
+  // Send an asynchronous message to the remote child via an actor.
+  // Note: use this only for messages through an actor. For old-style
+  // messages, use the message manager. If 'all' is true, then send
+  // a message to all descendant processes.
+  sendMessageToActor(messageName, args, actorName, all) {
+    if (!this.frameLoader) {
+      return;
+    }
+
+    let windowGlobal = this.browsingContext.currentWindowGlobal;
+    if (!windowGlobal) {
+      // Workaround for bug 1523638 where about:blank is loaded in a tab.
+      if (messageName == "Browser:AppTab") {
+        setTimeout(() => { this.sendMessageToActor(messageName, args, actorName); }, 0);
+      }
+      return;
+    }
+
+    function sendToChildren(browsingContext, checkRoot) {
+      let windowGlobal = browsingContext.currentWindowGlobal;
+      if (windowGlobal && (!checkRoot || windowGlobal.isProcessRoot)) {
+        windowGlobal.getActor(actorName).sendAsyncMessage(messageName, args);
+      }
+
+      if (all) {
+        let contexts = browsingContext.getChildren();
+        for (let context of contexts) {
+          sendToChildren(context, true);
+        }
+      }
+    }
+
+    sendToChildren(this.browsingContext, false);
+  }
 }
 
 MozXULElement.implementCustomInterface(MozBrowser, [Ci.nsIBrowser]);