Add UseCounters for Event.cancelBubble behavior.

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 7e6f186cff66ae4160d2e8dac263c86a9f771c89..3aadfc5cff162360dc751c41aab08c19d7bb9857 100644
--- a/third_party/WebKit/Source/core/events/Event.h
+++ b/third_party/WebKit/Source/core/events/Event.h
@@ -179,8 +179,8 @@ public:
     bool defaultHandled() const { return m_defaultHandled; }
     void setDefaultHandled() { m_defaultHandled = true; }
 
-    bool cancelBubble() const { return m_cancelBubble; }
-    void setCancelBubble(bool cancel) { m_cancelBubble = cancel; }
+    bool cancelBubble(ExecutionContext* = nullptr) const { return m_cancelBubble; }
+    void setCancelBubble(ExecutionContext*, bool);
 
     Event* underlyingEvent() const { return m_underlyingEvent.get(); }
     void setUnderlyingEvent(Event*);