Bug 1585819 - Restrict loading XBL bindings from WrapObject to the little amount of XUL elements that remain with bindings. r=bzbarsky

People keep shooting themselves in the feet because of this codepath and writing
slow code.

There are just a few elements with bindings left, so just check those.

Also simplify a bit the code. The XUL element + tagname check should be pretty
fast now, and ComputedStyle objects no longer keep weak pointers to pres
contexts and such, so can be safely kept on a RefPtr across an style flush.

Differential Revision: https://phabricator.services.mozilla.com/D47995

dom/base/CustomElementRegistry.h

@@ -371,16 +371,6 @@ class CustomElementRegistry final : public nsISupports, public nsWrapperCache {
   };
 
  public:
-  /**
-   * Returns whether there's a definition that is likely to match this type
-   * atom. This is not exact, so should only be used for optimization, but it's
-   * good enough to prove that the chrome code doesn't need an XBL binding.
-   */
-  bool IsLikelyToBeCustomElement(nsAtom* aTypeAtom) const {
-    return mCustomDefinitions.GetWeak(aTypeAtom) ||
-           mElementCreationCallbacks.GetWeak(aTypeAtom);
-  }
-
   /**
    * Looking up a custom element definition.
    * https://html.spec.whatwg.org/#look-up-a-custom-element-definition

dom/base/Element.cpp

@@ -517,48 +517,26 @@ void Element::ClearStyleStateLocks() {
   NotifyStyleStateChange(locks.mLocks);
 }
 
-static bool IsLikelyCustomElement(const nsXULElement& aElement) {
+static bool MayNeedToLoadXBLBinding(const Element& aElement) {
-  const CustomElementData* data = aElement.GetCustomElementData();
+  if (!aElement.IsAnyOfXULElements(nsGkAtoms::panel, nsGkAtoms::textbox,
-  if (!data) {
+                                   nsGkAtoms::arrowscrollbox)) {
+    // Other elements no longer have XBL bindings. Please don't add to the list
+    // above unless completely necessary.
     return false;
   }
-
+  if (!aElement.IsInComposedDoc()) {
-  const CustomElementRegistry* registry =
-      nsContentUtils::GetCustomElementRegistry(aElement.OwnerDoc());
-  if (!registry) {
-    return false;
-  }
-
-  return registry->IsLikelyToBeCustomElement(data->GetCustomElementType());
-}
-
-static bool MayNeedToLoadXBLBinding(const Document& aDocument,
-                                    const Element& aElement) {
-  auto* xulElem = nsXULElement::FromNode(aElement);
-  if (!xulElem) {
     return false;
   }
   // If we have a frame, the frame has already loaded the binding.
-  // Otherwise, don't do anything else here unless we're dealing with XUL.
+  if (aElement.GetPrimaryFrame() || !aElement.OwnerDoc()->GetPresShell()) {
-  if (!aDocument.GetPresShell() || aElement.GetPrimaryFrame()) {
     return false;
   }
-  return !IsLikelyCustomElement(*xulElem);
+  // If we have a binding, well..
+  if (aElement.GetXBLBinding()) {
+    return false;
   }
-
+  // We need to try.
-StyleUrlOrNone Element::GetBindingURL(Document* aDocument) {
+  return true;
-  if (!MayNeedToLoadXBLBinding(*aDocument, *this)) {
-    return StyleUrlOrNone::None();
-  }
-
-  // Get the computed -moz-binding directly from the ComputedStyle
-  RefPtr<ComputedStyle> style =
-      nsComputedDOMStyle::GetComputedStyleNoFlush(this, nullptr);
-  if (!style) {
-    return StyleUrlOrNone::None();
-  }
-
-  return style->StyleDisplay()->mBinding;
 }
 
 JSObject* Element::WrapObject(JSContext* aCx,
@@ -568,43 +546,26 @@ JSObject* Element::WrapObject(JSContext* aCx,
     return nullptr;
   }
 
-  if (XRE_IsContentProcess() && !NodePrincipal()->IsSystemPrincipal()) {
+  if (!MayNeedToLoadXBLBinding(*this)) {
-    // We don't use XBL in content privileged content processes.
     return obj;
   }
 
-  Document* doc = GetComposedDoc();
+  RefPtr<ComputedStyle> style =
-  if (!doc) {
+      nsComputedDOMStyle::GetComputedStyleNoFlush(this, nullptr);
-    // There's no baseclass that cares about this call so we just
+  if (!style) {
-    // return here.
     return obj;
   }
 
-  // We must ensure that the XBL Binding is installed before we hand
+  // We have a binding that must be installed.
-  // back this object.
+  const StyleUrlOrNone& computedBinding = style->StyleDisplay()->mBinding;
-
+  if (!computedBinding.IsUrl()) {
-  if (HasFlag(NODE_MAY_BE_IN_BINDING_MNGR) && GetXBLBinding()) {
-    // There's already a binding for this element so nothing left to
-    // be done here.
-
-    // In theory we could call ExecuteAttachedHandler here when it's safe to
-    // run script if we also removed the binding from the PAQ queue, but that
-    // seems like a scary change that would mostly just add more
-    // inconsistencies.
     return obj;
   }
 
-  // Make sure the ComputedStyle goes away _before_ we load the binding
+  auto& url = computedBinding.AsUrl();
-  // since that can destroy the relevant presshell.
-
-  {
-    StyleUrlOrNone result = GetBindingURL(doc);
-    if (result.IsUrl()) {
-      auto& url = result.AsUrl();
   nsCOMPtr<nsIURI> uri = url.GetURI();
   nsCOMPtr<nsIPrincipal> principal = url.ExtraData().Principal();
 
-      // We have a binding that must be installed.
   nsXBLService* xblService = nsXBLService::GetInstance();
   if (!xblService) {
     dom::Throw(aCx, NS_ERROR_NOT_AVAILABLE);
@@ -623,8 +584,6 @@ JSObject* Element::WrapObject(JSContext* aCx,
                             &nsXBLBinding::ExecuteAttachedHandler));
     }
   }
-    }
-  }
 
   return obj;
 }

dom/base/Element.h

@@ -459,8 +459,6 @@ class Element : public FragmentOrElement {
     }
   }
 
-  mozilla::StyleUrlOrNone GetBindingURL(Document* aDocument);
-
   Directionality GetComputedDirectionality() const;
 
   static const uint32_t kAllServoDescendantBits =

xpcom/ds/StaticAtoms.py

@@ -143,6 +143,7 @@ STATIC_ATOMS = [
     Atom("aria_valuemin", "aria-valuemin"),
     Atom("aria_valuenow", "aria-valuenow"),
     Atom("arrow", "arrow"),
+    Atom("arrowscrollbox", "arrowscrollbox"),
     Atom("article", "article"),
     Atom("as", "as"),
     Atom("ascending", "ascending"),