Add UMA metric for tracking root level listeners for blocking touch.

third_party/WebKit/Source/core/events/TouchEvent.h

 /*
  * Copyright 2008, The Android Open Source Project
  * Copyright (C) 2012 Research In Motion Limited. 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 copyright
@@ skipping 64 matching lines @@
     void setChangedTouches(TouchList* changedTouches) { m_changedTouches = changedTouches; }
 
     bool causesScrollingIfUncanceled() const { return m_causesScrollingIfUncanceled; }
 
     bool isTouchEvent() const override;
 
     const AtomicString& interfaceName() const override;
 
     void preventDefault() override;
 
+    void doneDispatchedEventAtCurrentTarget() override;
+
     EventDispatchMediator* createMediator() override;
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     TouchEvent();
     TouchEvent(TouchList* touches, TouchList* targetTouches,
         TouchList* changedTouches, const AtomicString& type,
         AbstractView*, PlatformEvent::Modifiers,
         bool cancelable, bool causesScrollingIfUncanceled,
         double platformTimeStamp);
     TouchEvent(const AtomicString&, const TouchEventInit&);
 
     Member<TouchList> m_touches;
     Member<TouchList> m_targetTouches;
     Member<TouchList> m_changedTouches;
     bool m_causesScrollingIfUncanceled;
+    bool m_previousDefaultPrevented;

[tdresser, 2016/05/17 14:56:54]

Previous what?

Maybe:
bool defaultPreventedBeforeCurrentTarget?

[dtapuska, 2016/05/17 20:50:13]

Done.

 };
 
 class TouchEventDispatchMediator final : public EventDispatchMediator {
 public:
     static TouchEventDispatchMediator* create(TouchEvent*);
 
 private:
     explicit TouchEventDispatchMediator(TouchEvent*);
     TouchEvent& event() const;
     DispatchEventResult dispatchEvent(EventDispatcher&) const override;
 };
 
 DEFINE_EVENT_TYPE_CASTS(TouchEvent);
 
 } // namespace blink
 
 #endif // TouchEvent_h