Revert 141514 - Remove CachingValueStore in favor of an async ValueStoreFrontend.

chrome/browser/value_store/value_store_frontend.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_VALUE_STORE_FRONTEND_H_
-#define CHROME_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_
-#pragma once
-
-#include <string>
-
-#include "base/callback.h"
-#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/threading/non_thread_safe.h"
-#include "base/values.h"
-
-// A frontend for a LeveldbValueStore, for use on the UI thread.
-class ValueStoreFrontend
-    : public base::SupportsWeakPtr<ValueStoreFrontend>,
-      public base::NonThreadSafe {
- public:
-  typedef base::Callback<void(scoped_ptr<base::Value>)> ReadCallback;
-
-  explicit ValueStoreFrontend(const FilePath& db_path);
-  ~ValueStoreFrontend();
-
-  // Retrieves a value from the database asynchronously, passing a copy to
-  // |callback| when ready. NULL is passed if no matching entry is found.
-  void Get(const std::string& key, const ReadCallback& callback);
-
-  // Sets a value with the given key.
-  void Set(const std::string& key, scoped_ptr<base::Value> value);
-
-  // Removes the value with the given key.
-  void Remove(const std::string& key);
-
- private:
-  class Backend;
-
-  // A helper class to manage lifetime of the backing ValueStore, which lives
-  // on the FILE thread.
-  scoped_refptr<Backend> backend_;
-
-  DISALLOW_COPY_AND_ASSIGN(ValueStoreFrontend);
-};
-
-#endif  // CHROME_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_