Implement an initial extension settings API.

chrome/browser/extensions/extension_settings_storage_cache.h

+// Copyright (c) 2011 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_EXTENSION_SETTINGS_STORAGE_CACHE_H_
+#define CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_STORAGE_CACHE_H_
+#pragma once
+
+#include "base/memory/scoped_ptr.h"
+#include "chrome/browser/extensions/extension_settings_storage.h"
+
+// Wraps a storage area with a cache.  Ownership of the delegate storage
+// will be taken by the cache.
+//
+// Calls to Get() will return from the cache if an entry is present, or be
+// passed to the delegate and the result cached if not.
+//
+// Calls to Set() / Clear() / Remove() are written through to the delegate,
+// then stored in the cache if successful.
+class ExtensionSettingsStorageCache : public ExtensionSettingsStorage {
+ public:
+  // Creates a cache around a delegate.  Ownership of the delegate is taken.
+  explicit ExtensionSettingsStorageCache(ExtensionSettingsStorage* delegate);
+  ~ExtensionSettingsStorageCache() {}
+
+  int type() { return delegate_->type() | CACHED; }
+
+  void Get(const std::string& key, Callback* callback);
+  void Get(const ListValue& keys, Callback* callback);
+  void Get(Callback* callback);
+  void Set(const std::string& key, const Value& value, Callback* callback);
+  void Set(const DictionaryValue& values, Callback* callback);
+  void Remove(const std::string& key, Callback* callback);
+  void Remove(const ListValue& keys, Callback* callback);
+  void Clear(Callback *callback);
+
+ private:
+  // Returns whether the value was found in the cache.
+  // Ownership of value is released to the caller and placed in value.
+  bool GetFromCache(const std::string& key, Value** value);
+
+  scoped_ptr<ExtensionSettingsStorage> delegate_;
+  DictionaryValue cache_;
+};
+
+#endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_STORAGE_CACHE_H_