Work around for HDMI audio output rediscovering transistion loss.

ash/system/audio/tray_audio_delegate.h

 // Copyright 2014 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 ASH_SYSTEM_AUDIO_TRAY_AUDIO_DELEGATE_H_
 #define ASH_SYSTEM_AUDIO_TRAY_AUDIO_DELEGATE_H_
 
 namespace ash {
 namespace system {
 
@@ skipping 29 matching lines @@
   virtual bool IsOutputAudioMuted() = 0;
 
   // Sets the mute state of the output device.
   virtual void SetOutputAudioIsMuted(bool is_muted) = 0;
 
   // Sets the volume level of the output device in the range 0%-100%
   virtual void SetOutputVolumeLevel(int level) = 0;
 
   // Sets the internal speaker's channel mode.
   virtual void SetInternalSpeakerChannelMode(AudioChannelMode mode) = 0;
+
+  // If necessary, sets the starting point for re-discovering the active HDMI
+  // output device caused by device entering/exiting docking mode, HDMI display
+  // changing resolution, or chromeos device suspend/resume. If
+  // |force_rediscovering| is true, it will force to set the starting point for
+  // re-discovering the active HDMI output device again if it has been in the
+  // middle of rediscovering the HDMI active output device.
+  virtual void SetActiveHDMIOutoutRediscoveringIfNecessary(
+      bool force_rediscovering) = 0;
 };
 
 }  // namespace system
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_AUDIO_TRAY_AUDIO_DELEGATE_H_