Add CHECKs to find root cause of Windows-only crash.

media/audio/win/waveout_output_win.h

 // Copyright (c) 2011 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 MEDIA_AUDIO_WIN_WAVEOUT_OUTPUT_WIN_H_
 #define MEDIA_AUDIO_WIN_WAVEOUT_OUTPUT_WIN_H_
 #pragma once
 
 #include <windows.h>
 #include <mmsystem.h>
@@ skipping 111 matching lines @@
   // Handle returned by RegisterWaitForSingleObject().
   base::win::ScopedHandle waiting_handle_;
 
   // Pointer to the allocated audio buffers, we allocate all buffers in one big
   // chunk. This object owns them.
   scoped_array<char> buffers_;
 
   // Lock used to avoid the conflict when callbacks are called simultaneously.
   base::Lock lock_;
 
+  // Temporary here, for CHECK().
+  DWORD thread_id_;
+
   DISALLOW_COPY_AND_ASSIGN(PCMWaveOutAudioOutputStream);
 };
 
 #endif  // MEDIA_AUDIO_WIN_WAVEOUT_OUTPUT_WIN_H_