Implement the renderer side of the mojo based local storage implementation.

content/renderer/dom_storage/local_storage_area.h

 // Copyright 2016 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 CONTENT_RENDERER_DOM_STORAGE_LOCAL_STORAGE_AREA_H_
 #define CONTENT_RENDERER_DOM_STORAGE_LOCAL_STORAGE_AREA_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "content/renderer/dom_storage/local_storage_cached_area.h"
@@ skipping 14 matching lines @@
   blink::WebString key(unsigned index) override;
   blink::WebString getItem(const blink::WebString& key) override;
   void setItem(const blink::WebString& key,
                const blink::WebString& value,
                const blink::WebURL& page_url,
                WebStorageArea::Result& result) override;
   void removeItem(const blink::WebString& key,
                   const blink::WebURL& page_url) override;
   void clear(const blink::WebURL& url) override;
 
+  const std::string& id() const { return id_; }
+
  private:
   scoped_refptr<LocalStorageCachedArea> cached_area_;
+  // A globally unique identifier for this storage area. It's used to pass the
+  // source storage area, if any, in mutation events.
+  std::string id_;
 
   DISALLOW_COPY_AND_ASSIGN(LocalStorageArea);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_DOM_STORAGE_LOCAL_STORAGE_AREA_H_