Merge 112363 - [chromium] Send wheel events to main thread even if we think nothing is scrollable

Source/WebKit/chromium/src/WebCompositorInputHandlerImpl.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 169 matching lines @@
         const WebMouseWheelEvent& wheelEvent = *static_cast<const WebMouseWheelEvent*>(&event);
         CCInputHandlerClient::ScrollStatus scrollStatus = m_inputHandlerClient->scrollBegin(IntPoint(wheelEvent.x, wheelEvent.y), CCInputHandlerClient::Wheel);
         switch (scrollStatus) {
         case CCInputHandlerClient::ScrollStarted: {
             TRACE_EVENT_INSTANT2("cc", "WebCompositorInputHandlerImpl::handleInput wheel scroll", "deltaX", -wheelEvent.deltaX, "deltaY", -wheelEvent.deltaY);
             m_inputHandlerClient->scrollBy(IntSize(-wheelEvent.deltaX, -wheelEvent.deltaY));
             m_inputHandlerClient->scrollEnd();
             return DidHandle;
         }
         case CCInputHandlerClient::ScrollIgnored:
-            return DropEvent;
+            // FIXME: This should be DropEvent, but in cases where we fail to properly sync scrollability it's safer to send the
+            // event to the main thread. Change back to DropEvent once we have synchronization bugs sorted out.
+            return DidNotHandle; 
         case CCInputHandlerClient::ScrollFailed:
             return DidNotHandle;
         }
     } else if (event.type == WebInputEvent::GestureScrollBegin) {
         ASSERT(!m_gestureScrollStarted);
         ASSERT(!m_expectScrollUpdateEnd);
 #ifndef NDEBUG
         m_expectScrollUpdateEnd = true;
 #endif
         const WebGestureEvent& gestureEvent = *static_cast<const WebGestureEvent*>(&event);
@@ skipping 139 matching lines @@
         // thread and run the rest of the wheels from there.
         // This can happen when flinging a page that contains a scrollable subarea that we can't
         // scroll on the thread if the fling starts outside the subarea but then is flung "under" the
         // pointer.
         // For now, just abort the fling.
         cancelCurrentFling();
     }
 }
 
 }