Remove did(Start|Stop)WorkerThread as it is not used.

public/platform/Platform.h

 /*
  * Copyright (C) 2012 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 579 matching lines @@
 
     // May return null if WebRTC functionality is not avaliable or out of resources.
     virtual WebMediaStreamCenter* createMediaStreamCenter(WebMediaStreamCenterClient*) { return 0; }
 
 
     // WebWorker ----------------------------------------------------------
 
     virtual void didStartWorkerRunLoop(const WebWorkerRunLoop&) { }
     virtual void didStopWorkerRunLoop(const WebWorkerRunLoop&) { }
 
-    virtual void didStartWorkerThread(WebThread*) { }
-    virtual void didStopWorkerThread(WebThread*) { }
-
     // WebCrypto ----------------------------------------------------------
 
     virtual WebCrypto* crypto() { return 0; }
 
 
     // Device Motion / Orientation / Light ----------------------------------------
 
     // Sets a Listener to listen for device motion data updates.
     // If null, the platform stops providing device motion data to the current listener.
     virtual void setDeviceMotionListener(blink::WebDeviceMotionListener*) { }
@@ skipping 30 matching lines @@
     virtual WebNotificationPresenter* notificationPresenter() { return 0; }
 
 
 protected:
     virtual ~Platform() { }
 };
 
 } // namespace blink
 
 #endif