Try not to let the AUHAL driver get stuck sending silence.

media/audio/mac/audio_auhal_mac.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.
 //
 // Implementation notes:
 //
 // - It is recommended to first acquire the native sample rate of the default
 //   output device and then use the same rate when creating this object.
 //   Use AudioManagerMac::HardwareSampleRate() to retrieve the sample rate.
 // - Calling Close() also leads to self destruction.
@@ skipping 127 matching lines @@
 
   // Volume level from 0 to 1.
   float volume_;
 
   // Fixed playout hardware latency in frames.
   double hardware_latency_frames_;
 
   // The flag used to stop the streaming.
   bool stopped_;
 
+  // The flag used to indicate if the AudioManager has been notified of a
+  // potential device change.  Reset to false during Start().
+  bool notified_for_possible_device_change_;
+
   // The input AudioUnit renders its data here.
   scoped_ptr<uint8[]> input_buffer_list_storage_;
   AudioBufferList* input_buffer_list_;
 
   // Holds the actual data for |input_buffer_list_|.
   scoped_ptr<AudioBus> input_bus_;
 
   // Container for retrieving data from AudioSourceCallback::OnMoreIOData().
   scoped_ptr<AudioBus> output_bus_;
 
   DISALLOW_COPY_AND_ASSIGN(AUHALStream);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_MAC_AUDIO_AUHAL_MAC_H_