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

content/renderer/input/main_thread_event_queue.h

Index: content/renderer/input/main_thread_event_queue.h
diff --git a/content/renderer/input/main_thread_event_queue.h b/content/renderer/input/main_thread_event_queue.h
index 0eb2d147f8970e9aac457503e80a691300fb5fa5..c50b279b948de1254640c00fd1ede2a4d23e2c90 100644
--- a/content/renderer/input/main_thread_event_queue.h
+++ b/content/renderer/input/main_thread_event_queue.h
@@ -100,7 +100,8 @@ class CONTENT_EXPORT MainThreadEventQueue {
   bool HandleEvent(const blink::WebInputEvent* event,
                    const ui::LatencyInfo& latency,
                    InputEventDispatchType dispatch_type,
-                   InputEventAckState ack_result);
+                   InputEventAckState ack_result,
+                   bool is_flinging = false);

[tdresser, 2016/05/09 19:48:45]

Can we plumb the information about whether a fling is active separately from the
handle event call?

We should be able to tell the main thread event queue when fling starts and
stops, instead of adding this bit.

[lanwei, 2016/05/12 11:50:36]

Done.

 
   // Call once the main thread has handled an outstanding |type| event
   // in flight.