Work around for HDMI audio output rediscovering transistion loss.

ash/system/audio/tray_audio.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_H_
 #define ASH_SYSTEM_AUDIO_TRAY_AUDIO_H_
 
 #include "ash/system/audio/audio_observer.h"
 #include "ash/system/tray/tray_image_item.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 13 matching lines @@
                   public AudioObserver,
                   public gfx::DisplayObserver {
  public:
   TrayAudio(SystemTray* system_tray,
             scoped_ptr<system::TrayAudioDelegate> audio_delegate);
   ~TrayAudio() override;
 
   static bool ShowAudioDeviceMenu();
 
  protected:
+  // Overridden from gfx::DisplayObserver.
+  void OnDisplayAdded(const gfx::Display& new_display) override;
+  void OnDisplayRemoved(const gfx::Display& old_display) override;
+  void OnDisplayMetricsChanged(const gfx::Display& display,
+                               uint32_t changed_metrics) override;
+
   virtual void Update();
 
   scoped_ptr<system::TrayAudioDelegate> audio_delegate_;
   tray::VolumeView* volume_view_;
 
   // True if VolumeView should be created for accelerator pop up;
   // Otherwise, it should be created for detailed view in ash tray bubble.
   bool pop_up_volume_view_;
 
  private:
   // Overridden from TrayImageItem.
   bool GetInitialVisibility() override;
 
   // Overridden from SystemTrayItem.
   views::View* CreateDefaultView(user::LoginStatus status) override;
   views::View* CreateDetailedView(user::LoginStatus status) override;
   void DestroyDefaultView() override;
   void DestroyDetailedView() override;
   bool ShouldHideArrow() const override;
   bool ShouldShowShelf() const override;
 
   // Overridden from AudioObserver.
   void OnOutputNodeVolumeChanged(uint64_t node_id, double volume) override;
   void OnOutputMuteChanged(bool mute_on) override;
   void OnAudioNodesChanged() override;
   void OnActiveOutputNodeChanged() override;
   void OnActiveInputNodeChanged() override;
 
-  // Overridden from gfx::DisplayObserver.
-  void OnDisplayAdded(const gfx::Display& new_display) override;
-  void OnDisplayRemoved(const gfx::Display& old_display) override;
-  void OnDisplayMetricsChanged(const gfx::Display& display,
-                               uint32_t changed_metrics) override;
-
   void ChangeInternalSpeakerChannelMode();
 
   DISALLOW_COPY_AND_ASSIGN(TrayAudio);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_AUDIO_TRAY_AUDIO_H_