Rewrite DefaultPrefStore for performance

base/prefs/value_map_pref_store.h

 // Copyright (c) 2012 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 BASE_PREFS_VALUE_MAP_PREF_STORE_H_
 #define BASE_PREFS_VALUE_MAP_PREF_STORE_H_
 
 #include <map>
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/observer_list.h"
 #include "base/prefs/base_prefs_export.h"
 #include "base/prefs/pref_store.h"
 #include "base/prefs/pref_value_map.h"
 
 // A basic PrefStore implementation that uses a simple name-value map for
 // storing the preference values.
 class BASE_PREFS_EXPORT ValueMapPrefStore : public PrefStore {
  public:
-  typedef std::map<std::string, base::Value*>::iterator iterator;
-  typedef std::map<std::string, base::Value*>::const_iterator const_iterator;
-
   ValueMapPrefStore();
 
   // PrefStore overrides:
   virtual ReadResult GetValue(const std::string& key,
                               const base::Value** value) const OVERRIDE;
   virtual void AddObserver(PrefStore::Observer* observer) OVERRIDE;
   virtual void RemoveObserver(PrefStore::Observer* observer) OVERRIDE;
   virtual size_t NumberOfObservers() const OVERRIDE;
 
-  iterator begin();
-  iterator end();
-  const_iterator begin() const;
-  const_iterator end() const;
-
  protected:
   virtual ~ValueMapPrefStore();
 
   // Store a |value| for |key| in the store. Also generates an notification if
   // the value changed. Assumes ownership of |value|, which must be non-NULL.
   void SetValue(const std::string& key, base::Value* value);
 
   // Remove the value for |key| from the store. Sends a notification if there
   // was a value to be removed.
   void RemoveValue(const std::string& key);
 
   // Notify observers about the initialization completed event.
   void NotifyInitializationCompleted();
 
  private:
   PrefValueMap prefs_;
 
   ObserverList<PrefStore::Observer, true> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(ValueMapPrefStore);
 };
 
 #endif  // BASE_PREFS_VALUE_MAP_PREF_STORE_H_