arc: Revamp the ArcBridgeService interface

components/arc/window_manager/arc_window_manager_bridge.h

Index: components/arc/window_manager/arc_window_manager_bridge.h
diff --git a/components/arc/window_manager/arc_window_manager_bridge.h b/components/arc/window_manager/arc_window_manager_bridge.h
index f206e5de449abf2c084b6fb4799635d72444ca0f..27a346d7c93ab7242469c030eb570e59109c159d 100644
--- a/components/arc/window_manager/arc_window_manager_bridge.h
+++ b/components/arc/window_manager/arc_window_manager_bridge.h
@@ -11,18 +11,20 @@
 #include "base/macros.h"
 #include "components/arc/arc_bridge_service.h"
 #include "components/arc/arc_service.h"
+#include "components/arc/instance_holder.h"
 
 namespace arc {
 
-class ArcWindowManagerBridge : public ArcService,
-                               public ArcBridgeService::Observer,
-                               public ash::ShellObserver {
+class ArcWindowManagerBridge
+    : public ArcService,
+      public InstanceHolder<mojom::WindowManagerInstance>::Observer,
+      public ash::ShellObserver {
  public:
   explicit ArcWindowManagerBridge(ArcBridgeService* bridge_service);
   ~ArcWindowManagerBridge() override;
 
-  // ArcBridgeService::Observer
-  void OnWindowManagerInstanceReady() override;
+  // InstanceHolder<mojom::WindowManagerInstance>::Observer
+  void OnInstanceReady() override;
 
   // Ash::Shell::ShellObserver
   void OnMaximizeModeStarted() override;