arc: Revamp the ArcBridgeService interface

components/arc/audio/arc_audio_bridge.h

Index: components/arc/audio/arc_audio_bridge.h
diff --git a/components/arc/audio/arc_audio_bridge.h b/components/arc/audio/arc_audio_bridge.h
index 5f88b1ab10be5d4914011d52dbeece9120162749..34cf4f1ce40866e89e0cfac50aa8a9571decaa04 100644
--- a/components/arc/audio/arc_audio_bridge.h
+++ b/components/arc/audio/arc_audio_bridge.h
@@ -11,20 +11,21 @@
 #include "chromeos/audio/cras_audio_handler.h"
 #include "components/arc/arc_bridge_service.h"
 #include "components/arc/arc_service.h"
+#include "components/arc/instance_holder.h"
 #include "mojo/public/cpp/bindings/binding.h"
 
 namespace arc {
 
 class ArcAudioBridge : public ArcService,
-                       public ArcBridgeService::Observer,
+                       public InstanceHolder<mojom::AudioInstance>::Observer,
                        public mojom::AudioHost,
                        public chromeos::CrasAudioHandler::AudioObserver {
  public:
   explicit ArcAudioBridge(ArcBridgeService* bridge_service);
   ~ArcAudioBridge() override;
 
-  // ArcBridgeService::Observer overrides.
-  void OnAudioInstanceReady() override;
+  // InstanceHolder<mojom::AudioInstance>::Observer overrides.
+  void OnInstanceReady() override;
 
   // mojom::AudioHost overrides.
   void ShowVolumeControls() override;