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

third_party/WebKit/Source/core/input/EventHandler.cpp

Index: third_party/WebKit/Source/core/input/EventHandler.cpp
diff --git a/third_party/WebKit/Source/core/input/EventHandler.cpp b/third_party/WebKit/Source/core/input/EventHandler.cpp
index e3cfaf7cb01c70fbe6631718c17cf2e5526dab3c..2d55c9a9186e2a92cadd07f3b028a6449366d764 100644
--- a/third_party/WebKit/Source/core/input/EventHandler.cpp
+++ b/third_party/WebKit/Source/core/input/EventHandler.cpp
@@ -275,6 +275,7 @@ EventHandler::EventHandler(LocalFrame* frame)
     , m_activeIntervalTimer(this, &EventHandler::activeIntervalTimerFired)
     , m_lastShowPressTimestamp(0)
     , m_deltaConsumedForScrollSequence(false)
+    , m_waitingForFirstTouchMove(false)
 {
 }
 
@@ -3654,6 +3655,14 @@ public:
 WebInputEventResult EventHandler::dispatchTouchEvents(const PlatformTouchEvent& event,
     HeapVector<TouchInfo>& touchInfos, bool freshTouchEvents, bool allTouchReleased)
 {
+    bool firstTouchMoveAfterTouchStart = false;
+    if (event.type() == PlatformEvent::TouchStart) {
+        m_waitingForFirstTouchMove = true;
+    } else if (event.type() == PlatformEvent::TouchMove) {
+        firstTouchMoveAfterTouchStart = m_waitingForFirstTouchMove;
+        m_waitingForFirstTouchMove = false;
+    }
+
     // Build up the lists to use for the 'touches', 'targetTouches' and
     // 'changedTouches' attributes in the JS event. See
     // http://www.w3.org/TR/touch-events/#touchevent-interface for how these
@@ -3738,7 +3747,7 @@ WebInputEventResult EventHandler::dispatchTouchEvents(const PlatformTouchEvent&
             RawPtr<TouchEvent> touchEvent = TouchEvent::create(
                 touches.get(), touchesByTarget.get(touchEventTarget), changedTouches[state].m_touches.get(),
                 eventName, touchEventTarget->toNode()->document().domWindow(),
-                event.getModifiers(), event.cancelable(), event.causesScrollingIfUncanceled(), event.timestamp());
+                event.getModifiers(), event.cancelable(), event.causesScrollingIfUncanceled(), firstTouchMoveAfterTouchStart, event.timestamp());
 
             eventResult = mergeEventResult(eventResult, toWebInputEventResult(touchEventTarget->dispatchEvent(touchEvent.get())));
         }