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

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

Index: third_party/WebKit/Source/core/events/Event.h
diff --git a/third_party/WebKit/Source/core/events/Event.h b/third_party/WebKit/Source/core/events/Event.h
index 3aadfc5cff162360dc751c41aab08c19d7bb9857..3711f59582b81aab4c4455ced17ba699c6f4975d 100644
--- a/third_party/WebKit/Source/core/events/Event.h
+++ b/third_party/WebKit/Source/core/events/Event.h
@@ -118,6 +118,8 @@ public:
     EventTarget* currentTarget() const;
     void setCurrentTarget(EventTarget* currentTarget) { m_currentTarget = currentTarget; }
 
+    virtual void doneDispatchingEventAtCurrentTarget();

[Rick Byers, 2016/05/18 18:37:18]

please add a comment to this function - i.e. document that it's only invoked
when listeners were actually invoked and it's probably a good idea to mention
that should only be used to influence metrics not functionality (observing the
presence of listeners is dangerous).

[Rick Byers, 2016/05/18 18:37:18]

nit: you could just inline the empty function here (consistent with the other
trivial functions nearby).

[dtapuska, 2016/05/19 16:11:21]

Done.

[dtapuska, 2016/05/19 16:11:21]

Done.

+
     unsigned short eventPhase() const { return m_eventPhase; }
     void setEventPhase(unsigned short eventPhase) { m_eventPhase = eventPhase; }