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

chrome/renderer/extensions/extension_helper.h

Index: chrome/renderer/extensions/extension_helper.h
diff --git a/chrome/renderer/extensions/extension_helper.h b/chrome/renderer/extensions/extension_helper.h
index fcb82b144bfcaeb6764bbe440b5472e9e2b2e208..6e8fc9772264a077d6aab0b350d9e0eb82d33376 100644
--- a/chrome/renderer/extensions/extension_helper.h
+++ b/chrome/renderer/extensions/extension_helper.h
@@ -80,7 +80,7 @@ class ExtensionHelper
       const base::DictionaryValue& source_tab,
       const ExtensionMsg_ExternalConnectionInfo& info);
   void OnExtensionDeliverMessage(int target_port_id,
-                                 const std::string& message);
+                                 const base::ListValue& message);
   void OnExtensionDispatchOnDisconnect(int port_id,
                                        const std::string& error_message);
   void OnExecuteCode(const ExtensionMsg_ExecuteCode_Params& params);