Attempt to fixed crash on stop mirroring by stopping render thread on a worker thread.

content/browser/renderer_host/media/video_capture_device_impl.h

 // Copyright 2013 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_BROWSER_RENDERER_HOST_VIDEO_CAPTURE_DEVICE_IMPL_H_
 #define CONTENT_BROWSER_RENDERER_HOST_VIDEO_CAPTURE_DEVICE_IMPL_H_
 
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
@@ skipping 101 matching lines @@
 
   // This should only be checked on the UI thread.
   bool started() const { return started_; }
 
   // Starts capturing. Returns true if succeeded.
   // Must be run on the UI BrowserThread.
   virtual bool Start(
       const scoped_refptr<ThreadSafeCaptureOracle>& oracle_proxy) = 0;
 
   // Stops capturing. Must be run on the UI BrowserThread.
-  virtual void Stop() = 0;
+  // |callback| is invoked after the capturing has stopped.
+  virtual void Stop(const base::Closure& callback) = 0;
 
  protected:
   bool started_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(VideoCaptureMachine);
 };
 
 // The "meat" of the video capture implementation.
 //
@@ skipping 49 matching lines @@
   // system with direct access to |client_|.
   scoped_refptr<ThreadSafeCaptureOracle> oracle_proxy_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoCaptureDeviceImpl);
 };
 
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_VIDEO_CAPTURE_DEVICE_IMPL_H_