Report LatencyInfo through trace buffer

ui/events/gestures/gesture_sequence.cc

Index: ui/events/gestures/gesture_sequence.cc
diff --git a/ui/events/gestures/gesture_sequence.cc b/ui/events/gestures/gesture_sequence.cc
index 83266856e8cecac1dbb3ebdb944a575ea2d684df..d364ed2301b6ba9dade68511be7be4529fb50e90 100644
--- a/ui/events/gestures/gesture_sequence.cc
+++ b/ui/events/gestures/gesture_sequence.cc
@@ -350,6 +350,32 @@ float CalibrateFlingVelocity(float velocity) {
     return std::min(nu * velocity, GestureConfiguration::fling_velocity_cap());
 }
 
+
+void UpdateGestureEventLatencyInfo(const TouchEvent& event,
+                                   GestureSequence::Gestures* gestures) {
+  // If the touch event does not cause any rendering scheduled, then
+  // 1) If the touch event does not generate any gesture event, its
+  //    LatencyInfo ends here.
+  // 2) If the touch event generates gesture events, its latencyinfo
+  //    is copied into the gesture events.
+  if (!event.latency()->FindLatency(
+          ui::INPUT_EVENT_LATENCY_RENDERING_SCHEDULED_COMPONENT, 0, NULL)) {
+    if (gestures->empty()) {
+      ui::LatencyInfo* touch_latency =
+          const_cast<ui::LatencyInfo*>(event.latency());
+      touch_latency->AddLatencyNumber(
+          ui::INPUT_EVENT_LATENCY_TERMINATED_TOUCH_COMPONENT, 0, 0);
+    } else {
+      GestureSequence::Gestures::iterator it = gestures->begin();
+      for (; it != gestures->end(); it++) {
+        (*it)->latency()->MergeWith(*event.latency());
+        // Inheriting the trace_id from the touch event's LatencyInfo
+        (*it)->latency()->trace_id = event.latency()->trace_id;
+      }
+    }
+  }
+}
+
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -596,12 +622,7 @@ GestureSequence::Gestures* GestureSequence::ProcessTouchEventForGesture(
     }
   }
 
-  const ui::LatencyInfo* touch_latency = event.latency();
-  Gestures::iterator it = gestures->begin();
-  for (; it != gestures->end(); it++) {
-    (*it)->latency()->MergeWith(*touch_latency);
-  }
-
+  UpdateGestureEventLatencyInfo(event, gestures.get());
   return gestures.release();
 }