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

content/renderer/input/input_handler_wrapper.cc

Index: content/renderer/input/input_handler_wrapper.cc
diff --git a/content/renderer/input/input_handler_wrapper.cc b/content/renderer/input/input_handler_wrapper.cc
index c8280e4a3164d0c0084b3450a9ae177d3d1c79d4..7678f9337c1c6c72ce3619d66b4ef7ee713a3971 100644
--- a/content/renderer/input/input_handler_wrapper.cc
+++ b/content/renderer/input/input_handler_wrapper.cc
@@ -51,6 +51,7 @@ blink::WebGestureCurve* InputHandlerWrapper::CreateFlingAnimationCurve(
     blink::WebGestureDevice deviceSource,
     const blink::WebFloatPoint& velocity,
     const blink::WebSize& cumulative_scroll) {
+  DidStartFlinging();
   return blink::Platform::current()->createFlingAnimationCurve(
       deviceSource, velocity, cumulative_scroll);
 }
@@ -68,6 +69,10 @@ void InputHandlerWrapper::DidOverscroll(
   input_handler_manager_->DidOverscroll(routing_id_, params);
 }
 
+void InputHandlerWrapper::DidStartFlinging() {
+  input_handler_manager_->DidStartFlinging(routing_id_);
+}
+
 void InputHandlerWrapper::DidStopFlinging() {
   input_handler_manager_->DidStopFlinging(routing_id_);
 }