Fix MediaDevices* tests dependency on BrowserThread globals after ~BrowserThreadImpl().

content/browser/renderer_host/media/media_stream_manager.cc

 // 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.
 
 #include "content/browser/renderer_host/media/media_stream_manager.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 1739 matching lines @@
       }
     }
   }
 }
 
 void MediaStreamManager::SetGenerateStreamCallbackForTesting(
     GenerateStreamTestCallback test_callback) {
   generate_stream_test_callback_ = test_callback;
 }
 
+#if defined(OS_WIN)
+void MediaStreamManager::FlushVideoCaptureThreadForTesting() {
+  video_capture_thread_.FlushForTesting();
+}
+#endif
+
 }  // namespace content