Implement an initial extension settings API.

chrome/browser/extensions/extension_settings_storage_cache.h

Index: chrome/browser/extensions/extension_settings_storage_cache.h
diff --git a/chrome/browser/extensions/extension_settings_storage_cache.h b/chrome/browser/extensions/extension_settings_storage_cache.h
new file mode 100644
index 0000000000000000000000000000000000000000..41c914f30ecbd19127ca6e6587f8140a5e766df2
--- /dev/null
+++ b/chrome/browser/extensions/extension_settings_storage_cache.h
@@ -0,0 +1,53 @@
+// 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/compiler_specific.h"
+#include "base/memory/weak_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);
+
+  virtual void DeleteSoon() OVERRIDE;
+
+  virtual void Get(const std::string& key, Callback* callback) OVERRIDE;
+  virtual void Get(const ListValue& keys, Callback* callback) OVERRIDE;
+  virtual void Get(Callback* callback) OVERRIDE;
+  virtual void Set(
+      const std::string& key, const Value& value, Callback* callback) OVERRIDE;
+  virtual void Set(const DictionaryValue& values, Callback* callback) OVERRIDE;
+  virtual void Remove(const std::string& key, Callback* callback) OVERRIDE;
+  virtual void Remove(const ListValue& keys, Callback* callback) OVERRIDE;
+  virtual void Clear(Callback *callback) OVERRIDE;
+
+ private:
+  ~ExtensionSettingsStorageCache() {}
+
+  // 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);
+
+  // Deleted in DeleteSoon().
+  ExtensionSettingsStorage* delegate_;
+  DictionaryValue cache_;
+  base::WeakPtrFactory<DictionaryValue> cache_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExtensionSettingsStorageCache);
+};
+
+#endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_STORAGE_CACHE_H_