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

content/renderer/input/main_thread_event_queue.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/input/main_thread_event_queue.h"
 
 namespace content {
 
 MainThreadEventQueue::MainThreadEventQueue(int routing_id,
                                            MainThreadEventQueueClient* client)
@@ skipping 53 matching lines @@
     PendingTouchEvent modified_dispatch_type_event =
         PendingTouchEvent(*static_cast<const blink::WebTouchEvent*>(event),
                           latency, dispatch_type);
     modified_dispatch_type_event.event.shouldForceBePassive = is_flinging;
 
     // Adjust the |dispatchType| on the event since the compositor
     // determined all event listeners are passive.
     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) {
       touch_events_.Queue(modified_dispatch_type_event);
     } else {
       if (non_blocking) {
         touch_events_.set_state(WebInputEventQueueState::ITEM_PENDING);
         client_->SendEventToMainThread(routing_id_,
                                        &modified_dispatch_type_event.event,
                                        latency, dispatch_type);
@@ skipping 31 matching lines @@
                                      event->type);
     } else {
       touch_events_.set_state(WebInputEventQueueState::ITEM_NOT_PENDING);
     }
   } else {
     NOTREACHED() << "Invalid passive event type";
   }
 }
 
 }  // namespace content