Add UMA/Telemetry stats for touch event latency

ui/base/latency_info.cc

 // 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.
 
 #include "ui/base/latency_info.h"
 
 #include <algorithm>
 
 namespace ui {
 
@@ skipping 40 matching lines @@
   if (event_count > 0 && new_count != 0) {
     // Do a weighted average, so that the new event_time is the average of
     // the times of events currently in this structure with the time passed
     // into this method.
     it->second.event_time += (time - it->second.event_time) * event_count /
         new_count;
     it->second.event_count = new_count;
   }
 }
 
-bool LatencyInfo::HasLatencyComponent(LatencyComponentType type,
-                                      int64 id) const {
-  return latency_components.find(std::make_pair(type, id)) !=
-      latency_components.end();
+bool LatencyInfo::FindLatency(LatencyComponentType type,
+                              int64 id,
+                              LatencyComponent* output) const {
+  LatencyMap::const_iterator it = latency_components.find(
+      std::make_pair(type, id));
+  if (it == latency_components.end())
+    return false;
+  if (output)
+    *output = it->second;
+  return true;
 }
 
 void LatencyInfo::Clear() {
   latency_components.clear();
 }
 
 }  // namespace ui