[DevTools] Switch from separate sendMessageToBackend method to using embedder.

Source/devtools/front_end/sdk/WorkerManager.js

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 182 matching lines @@
 
         var message = event.data;
         this.dispatch(message);
     },
 
     /**
      * @param {!Object} messageObject
      */
     sendMessage: function(messageObject)
     {
-        window.opener.postMessage({workerId: this._workerId, command: "sendMessageToBackend", message: messageObject}, "*");
+        window.opener.postMessage({workerId: this._workerId, command: "sendMessageToWorker", message: messageObject}, "*");
     },
 
     __proto__: InspectorBackendClass.Connection.prototype
 }