arc: Revamp the ArcBridgeService interface

chrome/browser/chromeos/arc/arc_downloads_watcher_service.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 CHROME_BROWSER_CHROMEOS_ARC_ARC_DOWNLOADS_WATCHER_SERVICE_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_ARC_DOWNLOADS_WATCHER_SERVICE_H_
 
 #include <memory>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "components/arc/arc_bridge_service.h"
 #include "components/arc/arc_service.h"
+#include "components/arc/instance_holder.h"
 
 namespace base {
 
 class FilePath;
 
 }  // namespace base
 
 namespace arc {
 
 // Watches Downloads directory and registers newly created media files to
 // Android MediaProvider.
-class ArcDownloadsWatcherService : public ArcService,
-                                   public ArcBridgeService::Observer {
+class ArcDownloadsWatcherService
+    : public ArcService,
+      public InstanceHolder<mojom::FileSystemInstance>::Observer {
  public:
   explicit ArcDownloadsWatcherService(ArcBridgeService* bridge_service);
   ~ArcDownloadsWatcherService() override;
 
-  // ArcBridgeService::Observer
-  void OnFileSystemInstanceReady() override;
-  void OnFileSystemInstanceClosed() override;
+  // InstanceHolder<mojom::FileSystemInstance>::Observer
+  void OnInstanceReady() override;
+  void OnInstanceClosed() override;
 
  private:
   class DownloadsWatcher;
 
   void StartWatchingDownloads();
   void StopWatchingDownloads();
 
   void OnDownloadsChanged(const std::vector<base::FilePath>& paths);
 
   std::unique_ptr<DownloadsWatcher> watcher_;
 
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate the weak pointers before any other members are destroyed.
   base::WeakPtrFactory<ArcDownloadsWatcherService> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcDownloadsWatcherService);
 };
 
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_ARC_DOWNLOADS_WATCHER_SERVICE_H_