Make sure send one WebTouchEvent ack per ui::TouchEvent

ui/events/gestures/motion_event_aura.cc

Index: ui/events/gestures/motion_event_aura.cc
diff --git a/ui/events/gestures/motion_event_aura.cc b/ui/events/gestures/motion_event_aura.cc
index 01df3f6042620f5dd945e786f91d93affda7a1db..65b4a492547aaac7ce052700689596ff60282474 100644
--- a/ui/events/gestures/motion_event_aura.cc
+++ b/ui/events/gestures/motion_event_aura.cc
@@ -182,9 +182,11 @@ void MotionEventAura::UpdateCachedAction(const TouchEvent& touch) {
       break;
     case ET_TOUCH_CANCELLED:
       set_action(ACTION_CANCEL);
+      set_action_index(GetIndexFromId(touch.touch_id()));

[tdresser, 2015/05/04 20:41:10]

This causes us to deviate from the Android implementation
(http://developer.android.com/reference/android/view/MotionEvent.html#getActio...),
which isn't ideal.

I think this change won't work correctly on Android.

[jdduke (slow), 2015/05/04 20:46:43]

Yeah, I'd prefer that we not overload the meaning of this property. In
particular, on Android, we get batched movement, so for multitouch all pointers
can move for a single event.

       break;
     case ET_TOUCH_MOVED:
       set_action(ACTION_MOVE);
+      set_action_index(GetIndexFromId(touch.touch_id()));
       break;
     default:
       NOTREACHED();