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

content/renderer/input/input_event_filter.h

Index: content/renderer/input/input_event_filter.h
diff --git a/content/renderer/input/input_event_filter.h b/content/renderer/input/input_event_filter.h
index 6457fb6116ceff1fa2fe81b10fc0632ad08bb7dd..ea948241d8d85ea82732ea508c3c17c0c3bbea62 100644
--- a/content/renderer/input/input_event_filter.h
+++ b/content/renderer/input/input_event_filter.h
@@ -66,6 +66,7 @@ class CONTENT_EXPORT InputEventFilter : public InputHandlerManagerClient,
   void DidOverscroll(int routing_id,
                      const DidOverscrollParams& params) override;
   void DidStopFlinging(int routing_id) override;
+  void DidStartFlinging(bool is_on_impl) override;
   void NotifyInputEventHandled(int routing_id,
                                blink::WebInputEvent::Type type) override;
 
@@ -114,6 +115,9 @@ class CONTENT_EXPORT InputEventFilter : public InputHandlerManagerClient,
   // bundled in the event ack, saving an IPC.  Note that we must continue
   // supporting overscroll IPC notifications due to fling animation updates.
   std::unique_ptr<DidOverscrollParams>* current_overscroll_params_;
+
+  bool is_flinging_on_main_;
+  bool is_flinging_on_impl_;
 };
 
 }  // namespace content