Unrevert r141537: Add extensions::StateStore and use that instead of

chrome/browser/value_store/caching_value_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 CHROME_BROWSER_VALUE_STORE_CACHING_VALUE_STORE_H_
-#define CHROME_BROWSER_VALUE_STORE_CACHING_VALUE_STORE_H_
-#pragma once
-
-#include <string>
-
-#include "base/file_path.h"
-#include "base/memory/ref_counted.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/memory/weak_ptr.h"
-#include "base/observer_list.h"
-#include "base/threading/non_thread_safe.h"
-#include "base/values.h"
-
-// Value store area with caching, backed by a LeveldbValueStore on the FILE
-// thread. The key/value store is flat with no path expansion, meaning "foo"
-// and "foo.bar" are completely separate keys.
-class CachingValueStore
-    : public base::SupportsWeakPtr<CachingValueStore>,
-      public base::NonThreadSafe {
- public:
-  class Observer {
-   public:
-    virtual ~Observer() {}
-
-    // Notification that the Store is ready to use.
-    virtual void OnInitializationComplete() = 0;
-  };
-
-  explicit CachingValueStore(const FilePath& db_path);
-  ~CachingValueStore();
-
-  // Retrieves a value from the cache, returning true if value with the given
-  // key exists. The returned value is a reference to the value in the cache,
-  // i.e. no copies are made.
-  bool Get(const std::string& key, const base::Value** result);
-
-  // Sets a value with the given key. Ownership of |value| is transferred to
-  // the store.
-  void Set(const std::string& key, base::Value* value);
-
-  // Removes the value with the given key.
-  void Remove(const std::string& key);
-
-  // Returns true if the store has finished initializing.
-  bool IsInitialized();
-
-  void AddObserver(Observer* observer);
-  void RemoveObserver(Observer* observer);
-
- private:
-  class Backend;
-
-  // Called when our backend finishes reading the database.
-  void OnBackendReady(scoped_ptr<base::DictionaryValue> values);
-
-  // A cache of the value store. This is always up-to-date, with changes
-  // persisted to disk as they are made.
-  scoped_ptr<base::DictionaryValue> cache_;
-
-  // A helper class to manage lifetime of the backing ValueStore, which lives
-  // on the FILE thread.
-  scoped_refptr<Backend> backend_;
-
-  ObserverList<Observer, true> observers_;
-
-  DISALLOW_COPY_AND_ASSIGN(CachingValueStore);
-};
-
-#endif  // CHROME_BROWSER_VALUE_STORE_CACHING_VALUE_STORE_H_