Replace std::map with base::SmallMap in ui::LatencyInfo

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 <map>
 #include <utility>
 #include <vector>
 
 #include "base/basictypes.h"
+#include "base/containers/small_map.h"
 #include "base/time/time.h"
 #include "ui/events/events_base_export.h"
 
 namespace ui {
 
 enum LatencyComponentType {
   // ---------------------------BEGIN COMPONENT-------------------------------
   // BEGIN COMPONENT is when we show the latency begin in chrome://tracing.
   // Timestamp when the input event is sent from RenderWidgetHost to renderer.
   INPUT_EVENT_LATENCY_BEGIN_RWH_COMPONENT,
@@ skipping 50 matching lines @@
     // Nondecreasing number that can be used to determine what events happened
     // in the component at the time this struct was sent on to the next
     // component.
     int64 sequence_number;
     // Average time of events that happened in this component.
     base::TimeTicks event_time;
     // Count of events that happened in this component
     uint32 event_count;
   };
 
+  // Empirically determined constant based on a typical scroll sequence.
+  enum { kTypicalMaxComponentsPerLatencyInfo = 6 };
+
   // Map a Latency Component (with a component-specific int64 id) to a
   // component info.
-  typedef std::map<std::pair<LatencyComponentType, int64>, LatencyComponent>
-      LatencyMap;
+  typedef base::SmallMap<
+      std::map<std::pair<LatencyComponentType, int64>, LatencyComponent>,
+      kTypicalMaxComponentsPerLatencyInfo> LatencyMap;
 
   LatencyInfo();
 
   ~LatencyInfo();
 
   // Returns true if the vector |latency_info| is valid. Returns false
   // if it is not valid and log the |referring_msg|.
   // This function is mainly used to check the latency_info vector that
   // is passed between processes using IPC message has reasonable size
   // so that we are confident the IPC message is not corrupted/compromised.
@@ skipping 39 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_