Add UMA/Telemetry stats for touch event 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>
 
@@ skipping 47 matching lines @@
   // Modifies the current sequence number and adds a certain number of events
   // for a specific component.
   void AddLatencyNumberWithTimestamp(LatencyComponentType component,
                                      int64 id,
                                      int64 component_sequence_number,
                                      base::TimeTicks time,
                                      uint32 event_count);
 
   void Clear();
 
+  LatencyMap::const_iterator GetLatencyComponent(LatencyComponentType type,

[Rick Byers, 2013/06/26 21:42:10]

Rather than return an iterator, may be easier to use as:
bool GetLatencyComponent(LatencyComponentType type, int64 id, LatencyComponent&
output) ??

[Yufeng Shen (Slow to review), 2013/06/26 23:02:26]

Done.

+                                                 int64 id) const {
+    return latency_components.find(std::make_pair(type, id));
+  }
+
   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_