Add UMA/Telemetry stats for end-to-end scroll latency

ui/base/latency_info.h

 // Copyright 2013 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.
 
 #ifndef UI_BASE_LATENCY_INFO_H_
 #define UI_BASE_LATENCY_INFO_H_
 
 #include <map>
 #include <utility>
 
 #include "base/basictypes.h"
 #include "base/time/time.h"
 #include "ui/base/ui_export.h"
 
 namespace ui {
 
 enum LatencyComponentType {
   // Timestamp when the input event is sent from RenderWidgetHost to renderer.
   INPUT_EVENT_LATENCY_RWH_COMPONENT,
   // Timestamp when the injected event is sent from RenderWidgetHost to
   // renderer. For example, in Aura, touch event's LatencyInfo is carried over
   // to the injected gesture event. So gesture event's
   // INPUT_EVENT_LATENCY_RWH_COMPONENT is the timestamp when its original touch
   // events is sent from RWH to renderer. In non-aura platform,
   // INPUT_EVENT_LATENCY_RWH_COMPONENT is the same as
   // INPUT_EVENT_LATENCY_INJECTED_RWH_COMPONENT.
+  // It is now only set for GestureScrollXXX events.

[Rick Byers, 2013/07/10 01:36:30]

Please just rename this to 'GestureScroll' instead of 'Injected' and update the
comments accordingly.  I think the code that looks for this will make more sense
then.

[Yufeng Shen (Slow to review), 2013/07/10 15:12:04]

Done.

   INPUT_EVENT_LATENCY_INJECTED_RWH_COMPONENT,
   // Original timestamp for input event (e.g. timestamp from kernel).
   INPUT_EVENT_LATENCY_ORIGINAL_COMPONENT,
   // Timestamp when the UI event is created.
   INPUT_EVENT_LATENCY_UI_COMPONENT,
   // Timestamp when the event is acked from renderer. This is currently set
   // only for touch events.
   INPUT_EVENT_LATENCY_ACKED_COMPONENT
 };
 
@@ skipping 46 matching lines @@
 
   LatencyMap latency_components;
 
   // This represents the final time that a frame is displayed it.
   base::TimeTicks swap_timestamp;
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_LATENCY_INFO_H_