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

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

Index: third_party/WebKit/Source/core/events/NodeEventContext.cpp
diff --git a/third_party/WebKit/Source/core/events/NodeEventContext.cpp b/third_party/WebKit/Source/core/events/NodeEventContext.cpp
index 318569f0c9229236f7ecfef73a15de0a23937329..3d6e52f851fc1575b07e44046df86ee6266e9a1b 100644
--- a/third_party/WebKit/Source/core/events/NodeEventContext.cpp
+++ b/third_party/WebKit/Source/core/events/NodeEventContext.cpp
@@ -50,8 +50,8 @@ DEFINE_TRACE(NodeEventContext)
 
 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());