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

third_party/WebKit/Source/core/events/NodeEventContext.cpp

 /*
  * Copyright (C) 2014 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 32 matching lines @@
 
 DEFINE_TRACE(NodeEventContext)
 {
     visitor->trace(m_node);
     visitor->trace(m_currentTarget);
     visitor->trace(m_treeScopeEventContext);
 }
 
 void NodeEventContext::handleLocalEvents(Event& event) const
 {
-    if (touchEventContext()) {
-        touchEventContext()->handleLocalEvents(event);
+    if (TouchEventContext* touchContext = touchEventContext()) {
+        touchContext->handleLocalEvents(event);
     } else if (relatedTarget()) {
         if (event.isMouseEvent()) {
             toMouseEvent(event).setRelatedTarget(relatedTarget());
         } else if (event.isFocusEvent()) {
             toFocusEvent(event).setRelatedTarget(relatedTarget());
         }
     }
     event.setTarget(target());
     event.setCurrentTarget(m_currentTarget.get());
     m_node->handleLocalEvents(event);
 }
 
 } // namespace blink