Implement scroll handler latency tracking

ui/events/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_EVENTS_LATENCY_INFO_H_
 #define UI_EVENTS_LATENCY_INFO_H_
 
 #include <utility>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/containers/small_map.h"
 #include "base/time/time.h"
 #include "ui/events/events_base_export.h"
 
 namespace ui {
 
 enum LatencyComponentType {
   // ---------------------------BEGIN COMPONENT-------------------------------
   // BEGIN COMPONENT is when we show the latency begin in chrome://tracing.
   // Timestamp when the input event is sent from RenderWidgetHost to renderer.
   INPUT_EVENT_LATENCY_BEGIN_RWH_COMPONENT,
   // Timestamp when the input event is received in plugin.
   INPUT_EVENT_LATENCY_BEGIN_PLUGIN_COMPONENT,
+  // Timestamp when a scroll update for the main thread is begun.
+  INPUT_EVENT_LATENCY_BEGIN_SCROLL_UPDATE_MAIN_COMPONENT,
   // ---------------------------NORMAL COMPONENT-------------------------------
   // Timestamp when the scroll update gesture event is sent from RWH to
   // renderer. In Aura, touch event's LatencyInfo is carried over to the 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_SCROLL_UPDATE_RWH_COMPONENT
   // is the same as INPUT_EVENT_LATENCY_RWH_COMPONENT.
   INPUT_EVENT_LATENCY_SCROLL_UPDATE_RWH_COMPONENT,
   // The original timestamp of the touch event which converts to scroll update.
   INPUT_EVENT_LATENCY_SCROLL_UPDATE_ORIGINAL_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,
   // This is special component indicating there is rendering scheduled for
   // the event associated with this LatencyInfo.
   INPUT_EVENT_LATENCY_RENDERING_SCHEDULED_COMPONENT,
+  // Timestamp when a scroll update is forwarded to the main thread.
+  INPUT_EVENT_LATENCY_FORWARD_SCROLL_UPDATE_TO_MAIN_COMPONENT,
   // Timestamp when the touch event is acked.
   INPUT_EVENT_LATENCY_ACKED_TOUCH_COMPONENT,
   // Frame number when a window snapshot was requested. The snapshot
   // is taken when the rendering results actually reach the screen.
   WINDOW_SNAPSHOT_FRAME_NUMBER_COMPONENT,
   // Frame number for a snapshot requested via
   // gpuBenchmarking.beginWindowSnapshotPNG
   // TODO(vkuzkokov): remove when patch adding this hits Stable
   WINDOW_OLD_SNAPSHOT_FRAME_NUMBER_COMPONENT,
   // Timestamp when a tab is requested to be shown.
@@ skipping 99 matching lines @@
   LatencyMap latency_components;
   // The unique id for matching the ASYNC_BEGIN/END trace event.
   int64 trace_id;
   // Whether a terminal component has been added.
   bool terminated;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_LATENCY_INFO_H_