Pass ui::LatencyInfo correct with unified gesture detector on Aura.

ui/events/gestures/gesture_provider_aura.cc

Index: ui/events/gestures/gesture_provider_aura.cc
diff --git a/ui/events/gestures/gesture_provider_aura.cc b/ui/events/gestures/gesture_provider_aura.cc
index 0db2e04f882d52dd017c8e31a33d5a6638eabea7..43aaf8ad5d4dad580602034435586d4ac2974cd1 100644
--- a/ui/events/gestures/gesture_provider_aura.cc
+++ b/ui/events/gestures/gesture_provider_aura.cc
@@ -22,6 +22,7 @@ GestureProviderAura::~GestureProviderAura() {}
 
 bool GestureProviderAura::OnTouchEvent(const TouchEvent& event) {
   last_touch_event_flags_ = event.flags();
+  last_touch_event_latency_info_ = *event.latency();
   bool pointer_id_is_active = false;
   for (size_t i = 0; i < pointer_state_.GetPointerCount(); ++i) {
     if (event.touch_id() != pointer_state_.GetPointerId(i))
@@ -80,6 +81,18 @@ void GestureProviderAura::OnGestureEvent(
                          // used when one finger is down, and will eventually
                          // be cleaned up. See crbug.com/366707.
                          1 << gesture.motion_event_id);
+
+  ui::LatencyInfo* gesture_latency = event.latency();
+  gesture_latency->CopyLatencyFrom(
+      last_touch_event_latency_info_,

[Yufeng Shen (Slow to review), 2014/06/02 18:27:04]

so is it guaranteed that the this gesture is derived from the last_touch_event ?

[tdresser, 2014/06/02 18:30:04]

Yes, although this would attribute a gesture fired on a timer to the most recent
touch, which may or may not be what we want.

[Yufeng Shen (Slow to review), 2014/06/02 18:43:35]

Is it easy to add some latency components to the gesture that is fired on timer
using the timestamp of the timer, e.g. the ui::INPUT_EVENT_LATENCY_UI_COMPONENT
component, and here we check only if we don't have the UI component then we copy
the latency from last_touch_event ?

[tdresser, 2014/06/02 20:04:11]

I've gone with the existing Aura behavior, which is to not set any latency
components for events triggered by a timeout.

+      ui::INPUT_EVENT_LATENCY_ORIGINAL_COMPONENT);
+  gesture_latency->CopyLatencyFrom(
+      last_touch_event_latency_info_,
+      ui::INPUT_EVENT_LATENCY_UI_COMPONENT);
+  gesture_latency->CopyLatencyFrom(
+      last_touch_event_latency_info_,
+      ui::INPUT_EVENT_LATENCY_ACKED_TOUCH_COMPONENT);
+
   client_->OnGestureEvent(&event);
 }