Add UMA metric for tracking listeners for blocking touch while fling is happening

content/renderer/input/main_thread_event_queue.cc

Index: content/renderer/input/main_thread_event_queue.cc
diff --git a/content/renderer/input/main_thread_event_queue.cc b/content/renderer/input/main_thread_event_queue.cc
index 15c83500253cecaca40140ffc35b5668a45f03c1..14151b26745d4fdc8699d90c8fe69b89ebc250c8 100644
--- a/content/renderer/input/main_thread_event_queue.cc
+++ b/content/renderer/input/main_thread_event_queue.cc
@@ -16,7 +16,8 @@ bool MainThreadEventQueue::HandleEvent(
     const blink::WebInputEvent* event,
     const ui::LatencyInfo& latency,
     InputEventDispatchType original_dispatch_type,
-    InputEventAckState ack_result) {
+    InputEventAckState ack_result,
+    bool is_flinging) {
   DCHECK(original_dispatch_type == DISPATCH_TYPE_BLOCKING ||
          original_dispatch_type == DISPATCH_TYPE_NON_BLOCKING);
   DCHECK(ack_result == INPUT_EVENT_ACK_STATE_SET_NON_BLOCKING ||
@@ -63,6 +64,7 @@ bool MainThreadEventQueue::HandleEvent(
     PendingTouchEvent modified_dispatch_type_event =
         PendingTouchEvent(*static_cast<const blink::WebTouchEvent*>(event),
                           latency, dispatch_type);
+    modified_dispatch_type_event.event.dispatchedDuringFling = is_flinging;
 
     // Adjust the |dispatchType| on the event since the compositor
     // determined all event listeners are passive.