Add UMA metric for tracking listeners for blocking touch while fling is happening

third_party/WebKit/public/web/WebInputEvent.h

 /*
  * Copyright (C) 2009 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 615 matching lines @@
 
     // Whether the event is blocking, non-blocking, all event
     // listeners were passive or was forced to be non-blocking.
     DispatchType dispatchType;
 
     // For a single touch, this is true after the touch-point has moved beyond
     // the platform slop region. For a multitouch, this is true after any
     // touch-point has moved (by whatever amount).
     bool movedBeyondSlopRegion;
 
+    // Whether there is an active fling animation when we dispatch the touch
+    // events.

[tdresser, 2016/05/09 19:48:45]

Maybe something like:

// Whether there was an active fling animation when the event was dispatched.

[lanwei, 2016/05/12 11:50:36]

Done.

+    bool dispatchedDuringFling;
+
     // A unique identifier for the touch event.
     uint32_t uniqueTouchEventId;
 
     WebTouchEvent()
         : WebInputEvent(sizeof(WebTouchEvent))
         , touchesLength(0)
         , dispatchType(Blocking)
         , movedBeyondSlopRegion(false)
+        , dispatchedDuringFling(false)
         , uniqueTouchEventId(0)
     {
     }
 };
 
 #pragma pack(pop)
 
 } // namespace blink
 
 #endif