Replace JSON (de)serialization of extension messages with direct Value pickling.

chrome/browser/extensions/message_handler.h

 // Copyright (c) 2012 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_MESSAGE_HANDLER_H_
 #define CHROME_BROWSER_EXTENSIONS_MESSAGE_HANDLER_H_
 
 #include <string>
 
 #include "content/public/browser/render_view_host_observer.h"
 
+namespace base {
+class ListValue;
+}
+
 namespace extensions {
 
 // Filters and dispatches extension-related IPC messages that arrive from
 // renderers. There is one of these objects for each RenderViewHost in Chrome.
 // Contrast this with extensions::TabHelper, which is only created for
 // WebContents.
 //
 // TODO(aa): Handling of content script messaging should be able to move to EFD
 // once there is an EFD for every RVHD where extension code can run. Then we
 // could eliminate this class. Right now, we don't end up with an EFD for tab
 // contents unless that tab contents is hosting chrome-extension:// URLs. That
 // still leaves content scripts. See also: crbug.com/80307.
 class MessageHandler : public content::RenderViewHostObserver {
  public:
   // |sender| is guaranteed to outlive this object.
   explicit MessageHandler(content::RenderViewHost* render_view_host);
   virtual ~MessageHandler();
 
   // RenderViewHostObserver overrides.
   virtual void RenderViewHostInitialized() OVERRIDE;
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
  private:
   // Message handlers.
-  void OnPostMessage(int port_id, const std::string& message);
+  void OnPostMessage(int port_id, const base::ListValue& message);
 
   DISALLOW_COPY_AND_ASSIGN(MessageHandler);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_MESSAGE_HANDLER_H_