arc: Revamp the ArcBridgeService interface

components/arc/obb_mounter/arc_obb_mounter_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_OBB_MOUNTER_ARC_OBB_MOUNTER_BRIDGE_H_
 #define COMPONENTS_ARC_OBB_MOUNTER_ARC_OBB_MOUNTER_BRIDGE_H_
 
 #include "base/macros.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 {
 
 // This class handles OBB mount/unmount requests from Android.
-class ArcObbMounterBridge : public ArcService,
-                            public ArcBridgeService::Observer,
-                            public mojom::ObbMounterHost {
+class ArcObbMounterBridge
+    : public ArcService,
+      public InstanceHolder<mojom::ObbMounterInstance>::Observer,
+      public mojom::ObbMounterHost {
  public:
   explicit ArcObbMounterBridge(ArcBridgeService* bridge_service);
   ~ArcObbMounterBridge() override;
 
-  // ArcBridgeService::Observer overrides:
-  void OnObbMounterInstanceReady() override;
+  // InstanceHolder<mojom::ObbMounterInstance>::Observer overrides:
+  void OnInstanceReady() override;
 
   // mojom::ObbMounterHost overrides:
   void MountObb(const mojo::String& obb_file,
                 const mojo::String& target_path,
                 int32_t owner_gid,
                 const MountObbCallback& callback) override;
   void UnmountObb(const mojo::String& target_path,
                   const UnmountObbCallback& callback) override;
 
  private:
   mojo::Binding<mojom::ObbMounterHost> binding_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcObbMounterBridge);
 };
 
 }  // namespace arc
 
 #endif  // COMPONENTS_ARC_OBB_MOUNTER_ARC_OBB_MOUNTER_BRIDGE_H_