Bug 1421351 - Queue chrome-only scrollend event in refresh driver scroll event queue instead of firing immediately. r=kats

MozReview-Commit-ID: KVQ5kp1t7NW

layout/generic/nsGfxScrollFrame.cpp

@@ -2107,6 +2107,9 @@ ScrollFrameHelper::~ScrollFrameHelper()
   if (mScrollEvent) {
     mScrollEvent->Revoke();
   }
+  if (mScrollEndEvent) {
+    mScrollEndEvent->Revoke();
+  }
 }
 
 /*
@@ -2186,7 +2189,7 @@ ScrollFrameHelper::CompleteAsyncScroll(const nsRect &aRange, nsAtom* aOrigin)
   // We are done scrolling, set our destination to wherever we actually ended
   // up scrolling to.
   mDestination = GetScrollPosition();
-  FireScrollEndEvent();
+  PostScrollEndEvent();
 }
 
 bool
@@ -4422,10 +4425,25 @@ ScrollFrameHelper::FireScrollPortEvent()
                                    mOuter->PresContext(), &event);
 }
 
+void
+ScrollFrameHelper::PostScrollEndEvent()
+{
+  if (mScrollEndEvent) {
+    return;
+  }
+
+  // The ScrollEndEvent constructor registers itself with the refresh driver.
+  mScrollEndEvent = new ScrollEndEvent(this);
+}
+
 void
 ScrollFrameHelper::FireScrollEndEvent()
 {
   MOZ_ASSERT(mOuter->GetContent());
+  MOZ_ASSERT(mScrollEndEvent);
+  mScrollEndEvent->Revoke();
+  mScrollEndEvent = nullptr;
+
   nsContentUtils::DispatchEventOnlyToChrome(mOuter->GetContent()->OwnerDoc(),
                                             mOuter->GetContent(),
                                             NS_LITERAL_STRING("scrollend"),
@@ -4821,6 +4839,22 @@ ScrollFrameHelper::ScrollEvent::Run()
   return NS_OK;
 }
 
+ScrollFrameHelper::ScrollEndEvent::ScrollEndEvent(ScrollFrameHelper* aHelper)
+  : Runnable("ScrollFrameHelper::ScrollEndEvent")
+  , mHelper(aHelper)
+{
+  mHelper->mOuter->PresContext()->RefreshDriver()->PostScrollEvent(this);
+}
+
+NS_IMETHODIMP
+ScrollFrameHelper::ScrollEndEvent::Run()
+{
+  if (mHelper) {
+    mHelper->FireScrollEndEvent();
+  }
+  return NS_OK;
+}
+
 void
 ScrollFrameHelper::FireScrollEvent()
 {

layout/generic/nsGfxScrollFrame.h

@@ -69,6 +69,7 @@ public:
     nsTArray<nsIAnonymousContentCreator::ContentInfo>& aElements);
   void AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements, uint32_t aFilter);
   nsresult FireScrollPortEvent();
+  void PostScrollEndEvent();
   void FireScrollEndEvent();
   void PostOverflowEvent();
   using PostDestroyData = nsIFrame::PostDestroyData;
@@ -131,6 +132,15 @@ public:
     ScrollFrameHelper* mHelper;
   };
 
+  class ScrollEndEvent : public Runnable {
+  public:
+    NS_DECL_NSIRUNNABLE
+    explicit ScrollEndEvent(ScrollFrameHelper* aHelper);
+    void Revoke() { mHelper = nullptr; }
+  private:
+    ScrollFrameHelper* mHelper;
+  };
+
   class AsyncScrollPortEvent : public Runnable {
   public:
     NS_DECL_NSIRUNNABLE
@@ -402,7 +412,7 @@ public:
 
   void SetTransformingByAPZ(bool aTransforming) {
     if (mTransformingByAPZ && !aTransforming) {
-      FireScrollEndEvent();
+      PostScrollEndEvent();
     }
     mTransformingByAPZ = aTransforming;
     if (!mozilla::css::TextOverflow::HasClippedOverflow(mOuter)) {
@@ -495,6 +505,7 @@ public:
   nsCOMPtr<nsIContent> mResizerContent;
 
   RefPtr<ScrollEvent> mScrollEvent;
+  RefPtr<ScrollEndEvent> mScrollEndEvent;
   nsRevocableEventPtr<AsyncScrollPortEvent> mAsyncScrollPortEvent;
   nsRevocableEventPtr<ScrolledAreaEvent> mScrolledAreaEvent;
   nsIFrame* mHScrollbarBox;