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>
 
@@ skipping 14 matching lines @@
   // ---------------------------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,
+  // The timestamp when the scroll event reached blink (e.g. a scroll handler).
+  INPUT_EVENT_LATENCY_SCROLL_UPDATE_BLINK_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 the touch event is acked.
   INPUT_EVENT_LATENCY_ACKED_TOUCH_COMPONENT,
   // Frame number when a window snapshot was requested. The snapshot
@@ skipping 104 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_