Add UMA metric to track the time saved on making events passive during fling

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 a16d2d462799976c571185c9855bd0f81ae8bb18..deb4318ddeb97c1081580229a03134ca072bf157 100644
--- a/content/renderer/input/main_thread_event_queue.cc
+++ b/content/renderer/input/main_thread_event_queue.cc
@@ -71,6 +71,12 @@ bool MainThreadEventQueue::HandleEvent(
     if (non_blocking) {
       modified_dispatch_type_event.event.dispatchType =
           blink::WebInputEvent::ListenersNonBlockingPassive;
+    } else {
+      if (modified_dispatch_type_event.event.type ==
+              blink::WebInputEvent::TouchStart &&
+          modified_dispatch_type_event.event.shouldForceBePassive)
+        modified_dispatch_type_event.event.dispatchType =
+            blink::WebInputEvent::ListenersForcedNonBlockingPassive;

[dtapuska, 2016/05/05 19:58:27]

If you set this then you need to make sure an ack is returned. I think this
might be the wrong place to do this. I think it needs to be an action in the
input_handler_proxy because it needs to take action on doing the default action
and then setting the event as being dispatched passively.

     }
 
     if (touch_events_.state() == WebInputEventQueueState::ITEM_PENDING) {