Routes touch ACK events to the correct GestureProvider

ui/events/gestures/gesture_recognizer_impl.h

Index: ui/events/gestures/gesture_recognizer_impl.h
diff --git a/ui/events/gestures/gesture_recognizer_impl.h b/ui/events/gestures/gesture_recognizer_impl.h
index a3e0f573e09719d65fcd6afcea1bfff69d361da2..26ba470e3f610c7fe7daecb13e20dc9a697a9f21 100644
--- a/ui/events/gestures/gesture_recognizer_impl.h
+++ b/ui/events/gestures/gesture_recognizer_impl.h
@@ -88,6 +88,12 @@ class EVENTS_EXPORT GestureRecognizerImpl : public GestureRecognizer,
   std::map<GestureConsumer*, std::unique_ptr<GestureProviderAura>>
       consumer_gesture_provider_;
 
+  // Maps an event via its |unique_event_id| to the corresponding gesture
+  // provider. This avoids any invalid reference while routing ACK for events

[tdresser, 2017/04/06 20:59:52]

ACK -> ACKs

[malaykeshav, 2017/04/07 01:07:59]

Doesnt each event have just 1 ACK?

[tdresser, 2017/04/07 12:33:00]

Yes, but you're referring to "events" and events have ACKs.

Any of:
"while routing an event's ACK" or
"while routing ACKs for events"

or even just:
"while routing an ACK"

would be fine.

+  // that may arise post |TransferEventsTo()| function call.
+  // See http://crbug.com/698843 for more info.
+  std::map<uint32_t, GestureProviderAura*> event_to_gesture_provider_;
+
   // |touch_id_target_| maps a touch-id to its target window.
   // touch-ids are removed from |touch_id_target_| on
   // ET_TOUCH_RELEASE and ET_TOUCH_CANCEL.