base: Add three helper functions to Values API.

chrome/browser/extensions/extension_accessibility_api.cc

 // 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.
 
 #include "chrome/browser/extensions/extension_tabs_module.h"
 
 #include "base/json/json_writer.h"
 #include "base/stl_util.h"
 #include "base/string_util.h"
 #include "base/values.h"
@@ skipping 191 matching lines @@
   // Get the serialized dict from the last focused control and return it.
   // However, if the dict is empty, that means we haven't seen any focus
   // events yet, so return null instead.
   ExtensionAccessibilityEventRouter *accessibility_event_router =
       ExtensionAccessibilityEventRouter::GetInstance();
   DictionaryValue *last_focused_control_dict =
       accessibility_event_router->last_focused_control_dict();
   if (last_focused_control_dict->size()) {
     result_.reset(last_focused_control_dict->DeepCopyWithoutEmptyChildren());
   } else {
-    result_.reset(Value::CreateNullValue());
+    result_.reset(base::NullValue());
   }
   return true;
 }