arc: Revamp the ArcBridgeService interface

components/arc/audio/arc_audio_bridge.h

 // Copyright 2016 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 COMPONENTS_ARC_AUDIO_ARC_AUDIO_BRIDGE_H_
 #define COMPONENTS_ARC_AUDIO_ARC_AUDIO_BRIDGE_H_
 
 #include <string>
 
 #include "base/macros.h"
 #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;
 
  private:
   mojo::Binding<mojom::AudioHost> binding_;
 
   chromeos::CrasAudioHandler* cras_audio_handler_ = nullptr;
 
   // chromeos::CrasAudioHandler::AudioObserver overrides.
   void OnAudioNodesChanged() override;
 
   void SendSwitchState(bool headphone_inserted, bool microphone_inserted);
 
   DISALLOW_COPY_AND_ASSIGN(ArcAudioBridge);
 };
 
 }  // namespace arc
 
 #endif  // COMPONENTS_ARC_AUDIO_ARC_AUDIO_BRIDGE_H_