Bug 1225412 Part 1 - Make AsyncEventDispatcher cancelable. r=smaug

Also I found that mBubbles are not initialized in the constructor in
AsyncEventDispatcher.cpp. I initialized those bool member variables
directly.

MozReview-Commit-ID: FiU4NKGJjU9

--HG--
extra : rebase_source : 1bcd5808b442eb726763602525977bc064ecc0ee

dom/events/AsyncEventDispatcher.cpp

@@ -23,7 +23,6 @@ using namespace dom;
 AsyncEventDispatcher::AsyncEventDispatcher(EventTarget* aTarget,
                                            WidgetEvent& aEvent)
   : mTarget(aTarget)
-  , mOnlyChromeDispatch(false)
 {
   MOZ_ASSERT(mTarget);
   RefPtr<Event> event =
@@ -37,6 +36,9 @@ AsyncEventDispatcher::AsyncEventDispatcher(EventTarget* aTarget,
 NS_IMETHODIMP
 AsyncEventDispatcher::Run()
 {
+  if (mCanceled) {
+    return NS_OK;
+  }
   RefPtr<Event> event = mEvent ? mEvent->InternalDOMEvent() : nullptr;
   if (!event) {
     event = NS_NewDOMEvent(mTarget, nullptr, nullptr);
@@ -52,6 +54,13 @@ AsyncEventDispatcher::Run()
   return NS_OK;
 }
 
+NS_IMETHODIMP
+AsyncEventDispatcher::Cancel()
+{
+  mCanceled = true;
+  return NS_OK;
+}
+
 nsresult
 AsyncEventDispatcher::PostDOMEvent()
 {

dom/events/AsyncEventDispatcher.h

@@ -19,13 +19,13 @@ class nsINode;
 namespace mozilla {
 
 /**
- * Use nsAsyncDOMEvent to fire a DOM event that requires safe a stable DOM.
+ * Use AsyncEventDispatcher to fire a DOM event that requires safe a stable DOM.
  * For example, you may need to fire an event from within layout, but
  * want to ensure that the event handler doesn't mutate the DOM at
  * the wrong time, in order to avoid resulting instability.
  */
 
-class AsyncEventDispatcher : public nsRunnable
+class AsyncEventDispatcher : public nsCancelableRunnable
 {
 public:
   /**
@@ -48,29 +48,28 @@ public:
     : mTarget(aTarget)
     , mEventType(aEventType)
     , mBubbles(aBubbles)
-    , mOnlyChromeDispatch(false)
   {
   }
 
   AsyncEventDispatcher(dom::EventTarget* aTarget, nsIDOMEvent* aEvent)
     : mTarget(aTarget)
     , mEvent(aEvent)
-    , mBubbles(false)
-    , mOnlyChromeDispatch(false)
   {
   }
 
   AsyncEventDispatcher(dom::EventTarget* aTarget, WidgetEvent& aEvent);
 
   NS_IMETHOD Run() override;
+  NS_IMETHOD Cancel() override;
   nsresult PostDOMEvent();
   void RunDOMEventWhenSafe();
 
   nsCOMPtr<dom::EventTarget> mTarget;
   nsCOMPtr<nsIDOMEvent> mEvent;
   nsString              mEventType;
-  bool                  mBubbles;
+  bool                  mBubbles = false;
-  bool                  mOnlyChromeDispatch;
+  bool                  mOnlyChromeDispatch = false;
+  bool                  mCanceled = false;
 };
 
 class LoadBlockingAsyncEventDispatcher final : public AsyncEventDispatcher