Bug 1492326, revert some of bug 1478372, so that callers need to get the custom interface from a custom element without using QueryInterface, r=peterv

dom/base/Element.cpp

@@ -3871,10 +3871,17 @@ void Element::GetCustomInterface(nsGetterAddRefs<T> aResult) {
   nsCOMPtr<nsISupports> iface = CustomElementRegistry::CallGetCustomInterface(
       this, NS_GET_TEMPLATE_IID(T));
   if (iface) {
-    CallQueryInterface(iface, static_cast<T**>(aResult));
+    if (NS_SUCCEEDED(CallQueryInterface(iface, static_cast<T**>(aResult)))) {
+      return;
     }
   }
 
+  // Otherwise, check the binding manager to see if it implements the interface
+  // for this element.
+  OwnerDoc()->BindingManager()->GetBindingImplementation(
+      this, NS_GET_TEMPLATE_IID(T), aResult);
+}
+
 void Element::ClearServoData(nsIDocument* aDoc) {
   MOZ_ASSERT(aDoc);
   if (HasServoData()) {

dom/xul/nsXULElement.cpp

@@ -296,16 +296,6 @@ NS_IMPL_RELEASE_INHERITED(nsXULElement, nsStyledElement)
 
 NS_INTERFACE_TABLE_HEAD_CYCLE_COLLECTION_INHERITED(nsXULElement)
   NS_ELEMENT_INTERFACE_TABLE_TO_MAP_SEGUE
-
-  nsCOMPtr<nsISupports> iface =
-      CustomElementRegistry::CallGetCustomInterface(this, aIID);
-  if (iface) {
-    iface->QueryInterface(aIID, aInstancePtr);
-    if (*aInstancePtr) {
-      return NS_OK;
-    }
-  }
-
 NS_INTERFACE_MAP_END_INHERITING(nsStyledElement)
 
 //----------------------------------------------------------------------

toolkit/content/customElements.js

@@ -200,7 +200,8 @@ const MozElementMixin = Base => class MozElement extends Base {
 
   /**
    * Indicate that a class defining a XUL element implements one or more
-   * XPCOM interfaces by adding a getCustomInterface implementation to it.
+   * XPCOM interfaces by adding a getCustomInterface implementation to it,
+   * as well as an implementation of QueryInterface.
    *
    * The supplied class should implement the properties and methods of
    * all of the interfaces that are specified.
@@ -218,6 +219,7 @@ const MozElementMixin = Base => class MozElement extends Base {
     }
 
     cls.prototype.customInterfaceNumbers = numbers;
+    cls.prototype.QueryInterface = ChromeUtils.generateQI(ifaces);
     cls.prototype.getCustomInterfaceCallback = function getCustomInterfaceCallback(iface) {
       if (numbers.has(iface.number)) {
         return getInterfaceProxy(this);