Improvements to uses of base::SmallMap

cc/scheduler/begin_frame_source.h

 // Copyright 2014 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 CC_SCHEDULER_BEGIN_FRAME_SOURCE_H_
 #define CC_SCHEDULER_BEGIN_FRAME_SOURCE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 265 matching lines @@
 
  private:
   void SourceChanged(const BeginFrameArgs& args);
 
   uint32_t current_source_id_ = 0;
   uint64_t current_sequence_number_ = BeginFrameArgs::kStartingFrameNumber;
   // Small sets, but order matters for intersection computation.
   base::flat_set<BeginFrameObserver*> observers_;
   base::flat_set<BeginFrameObserver*> finished_observers_;
   bool observers_had_damage_ = false;
-  base::SmallMap<std::map<BeginFrameObserver*, uint64_t>, 4>
+  base::flat_map<BeginFrameObserver*, uint64_t>
       latest_confirmed_sequence_numbers_;
 
   DISALLOW_COPY_AND_ASSIGN(BeginFrameObserverAckTracker);
 };
 
 class CC_EXPORT ExternalBeginFrameSourceClient {
  public:
   // Only called when changed.  Assumed false by default.
   virtual void OnNeedsBeginFrames(bool needs_begin_frames) = 0;
   // Called when all observers have completed a frame.
@@ skipping 32 matching lines @@
   bool frame_active_ = false;
   BeginFrameObserverAckTracker ack_tracker_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ExternalBeginFrameSource);
 };
 
 }  // namespace cc
 
 #endif  // CC_SCHEDULER_BEGIN_FRAME_SOURCE_H_