Add a Restore() method to ValueStore and make StorageAPI use it

chrome/browser/extensions/api/storage/settings_storage_quota_enforcer.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_EXTENSIONS_API_STORAGE_SETTINGS_STORAGE_QUOTA_ENFORCER_H_
 #define CHROME_BROWSER_EXTENSIONS_API_STORAGE_SETTINGS_STORAGE_QUOTA_ENFORCER_H_
 
 #include "base/compiler_specific.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/value_store/value_store.h"
@@ skipping 28 matching lines @@
   virtual ReadResult Get() OVERRIDE;
   virtual WriteResult Set(
       WriteOptions options,
       const std::string& key,
       const base::Value& value) OVERRIDE;
   virtual WriteResult Set(
       WriteOptions options, const base::DictionaryValue& values) OVERRIDE;
   virtual WriteResult Remove(const std::string& key) OVERRIDE;
   virtual WriteResult Remove(const std::vector<std::string>& keys) OVERRIDE;
   virtual WriteResult Clear() OVERRIDE;
+  virtual bool Restore() OVERRIDE;
+  virtual bool RestoreKey(const std::string& key) OVERRIDE;
+
+  ValueStore* get_delegate_for_test() { return delegate_.get(); }
 
  private:
+  // Calculate the current usage for the database.
+  void CalculateUsage();
+
   // Limits configuration.
   const Limits limits_;
 
   // The delegate storage area.
   scoped_ptr<ValueStore> const delegate_;
 
   // Total bytes in used by |delegate_|. Includes both key lengths and
   // JSON-encoded values.
   size_t used_total_;
 
   // Map of item key to its size, including the key itself.
   std::map<std::string, size_t> used_per_setting_;
 
   DISALLOW_COPY_AND_ASSIGN(SettingsStorageQuotaEnforcer);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_STORAGE_SETTINGS_STORAGE_QUOTA_ENFORCER_H_