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 45 matching lines @@
                         int64 component_sequence_number);
 
   // 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);
 
+  // Returns true if the a component with |type| and |id| is found in
+  // the latency_components and the component is stored to |output|.
+  // Returns false if no such component is found.
+  bool FindLatency(LatencyComponentType type,

[sadrul, 2013/06/27 17:44:01]

Merge this with HasLatency

[Yufeng Shen (Slow to review), 2013/06/27 19:01:03]

Done.

+                   int64 id,
+                   LatencyComponent* output) const;
+
   void Clear();
 
   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_