Add a callback to RemoteFileSyncService for reporting errors.

chrome/browser/sync_file_system/remote_file_sync_service.h

 // Copyright (c) 2012 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_SYNC_FILE_SYSTEM_REMOTE_FILE_SYNC_SERVICE_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_REMOTE_FILE_SYNC_SERVICE_H_
 
 #include "base/basictypes.h"
 #include "webkit/fileapi/file_system_url.h"
 #include "webkit/fileapi/syncable/sync_callbacks.h"
@@ skipping 14 matching lines @@
   class Observer {
    public:
     Observer() {}
     virtual ~Observer() {}
 
     // This is called when there're one or more remote changes available.
     // |pending_changes_hint| indicates the pending queue length to help sync
     // scheduling but the value may not be accurately reflect the real-time
     // value.
     virtual void OnRemoteChangeAvailable(int64 pending_changes_hint) = 0;
+
+    // This is called when RemoteFileSyncService changes its status.
+    virtual void OnRemoteSyncStatusChanged(
+        fileapi::SyncStatusCode new_status) {}
+
    private:
     DISALLOW_COPY_AND_ASSIGN(Observer);
   };
 
   RemoteFileSyncService() {}
   virtual ~RemoteFileSyncService() {}
 
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
 
   // Registers |origin| to track remote side changes for the |origin|.
-  virtual void RegisterOriginForTrackingChanges(const GURL& origin) = 0;
+  // Upon completion, invokes |callback| if it's non-empty.
+  virtual void RegisterOriginForTrackingChanges(
+      const GURL& origin,
+      const fileapi::SyncStatusCallback& callback) = 0;
 
   // Unregisters |origin| to track remote side changes for the |origin|.
-  virtual void UnregisterOriginForTrackingChanges(const GURL& origin) = 0;
+  // Upon completion, invokes |callback| if it's non-empty.
+  virtual void UnregisterOriginForTrackingChanges(
+      const GURL& origin,
+      const fileapi::SyncStatusCallback& callback) = 0;
 
   // Called by the sync engine to process one remote change.
   // After a change is processed |callback| will be called (to return
   // the control to the sync engine).
   virtual void ProcessRemoteChange(
       RemoteChangeProcessor* processor,
       const fileapi::SyncFileCallback& callback) = 0;
 
   // Returns a LocalChangeProcessor that applies a local change to the remote
   // storage backed by this service.
   virtual LocalChangeProcessor* GetLocalChangeProcessor() = 0;
 
   // Returns a list of conflicting files for the given origin.
   virtual void GetConflictFiles(
       const GURL& origin,
       const fileapi::SyncFileSetCallback& callback) = 0;
 
   // Returns the metadata of a remote file pointed by |url|.
   virtual void GetRemoteFileMetadata(
       const fileapi::FileSystemURL& url,
       const fileapi::SyncFileMetadataCallback& callback) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(RemoteFileSyncService);
 };
 
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_REMOTE_FILE_SYNC_SERVICE_H_