Add UMA/Telemetry stats for touch event latency

ui/base/latency_info.cc

Index: ui/base/latency_info.cc
diff --git a/ui/base/latency_info.cc b/ui/base/latency_info.cc
index f87f6dfac23f6880d895fc7ed1632cdbd51380a3..459fc2ab689a3183eede3c51a43042c2542a1c83 100644
--- a/ui/base/latency_info.cc
+++ b/ui/base/latency_info.cc
@@ -58,10 +58,16 @@ void LatencyInfo::AddLatencyNumberWithTimestamp(LatencyComponentType component,
   }
 }
 
-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() {