Add thread safety to AudioManagerBase to protect access to the audio thread member variable.

media/audio/audio_output_proxy.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_AUDIO_OUTPUT_PROXY_H_
 #define MEDIA_AUDIO_AUDIO_OUTPUT_PROXY_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
+#include "base/threading/non_thread_safe.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_parameters.h"
 
 class AudioOutputDispatcher;
 
 // AudioOutputProxy is an audio otput stream that uses resources more
 // efficiently than a regular audio output stream: it opens audio
 // device only when sound is playing, i.e. between Start() and Stop()
 // (there is still one physical stream per each audio output proxy in
 // playing state).
 //
 // AudioOutputProxy uses AudioOutputDispatcher to open and close
 // physical output streams.
-class MEDIA_EXPORT AudioOutputProxy : public AudioOutputStream {
+class MEDIA_EXPORT AudioOutputProxy :

[scherkus (not reviewing), 2012/01/19 01:39:59]

nit: initializer list format

class Foo
    : public Bar,
      public Baz, {
  // ....
};

+    public AudioOutputStream,
+    public NON_EXPORTED_BASE(base::NonThreadSafe) {
  public:
   // Caller keeps ownership of |dispatcher|.
   explicit AudioOutputProxy(AudioOutputDispatcher* dispatcher);
 
   // AudioOutputStream interface.
   virtual bool Open() OVERRIDE;
   virtual void Start(AudioSourceCallback* callback) OVERRIDE;
   virtual void Stop() OVERRIDE;
   virtual void SetVolume(double volume) OVERRIDE;
   virtual void GetVolume(double* volume) OVERRIDE;
@@ skipping 18 matching lines @@
   AudioOutputStream* physical_stream_;
 
   // Need to save volume here, so that we can restore it in case the stream
   // is stopped, and then started again.
   double volume_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioOutputProxy);
 };
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_PROXY_H_