WORK IN PROGRESS.

chrome/browser/extensions/extension_settings_storage.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_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_STORAGE_H_
 #pragma once
 
 #include "base/values.h"
 
@@ skipping 12 matching lines @@
     virtual ~Callback() {}
 
     // Indicates the storage operation was successful.  Settings value will be
     // non-NULL.  Ownership is passed to the callback.
     virtual void OnSuccess(DictionaryValue* settings) = 0;
 
     // Indicates the storage operation failed.  Messages describes the failure.
     virtual void OnFailure(const std::string& message) = 0;
   };
 
+  // Callback which does nothing.
+  class NoopCallback : public Callback {
+   public:
+    virtual ~NoopCallback() {}
+    virtual void OnSuccess(DictionaryValue* s) OVERRIDE { delete s; }
+    virtual void OnFailure(const std::string& message) OVERRIDE {}
+  };
+
   // The different types of extension settings storage.
   enum Type {
     NONE,
     NOOP,
     LEVELDB
   };
 
   virtual ~ExtensionSettingsStorage() {}
 
   // Destroys this settings storage object.  This is needed as a separate
@@ skipping 31 matching lines @@
   // Removes multiple keys from the map.  Callback with a dictionary mapping
   // each key to its new value; on success, this will be an empty map.
   virtual void Remove(const ListValue& keys, Callback* callback) = 0;
 
   // Clears the storage.  Callback with a dictionary mapping every key in
   // storage to its value; on success, this will be an empty map.
   virtual void Clear(Callback *callback) = 0;
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_STORAGE_H_