drive: Support offline delete

chrome/browser/chromeos/drive/file_system/operation_observer.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_CHROMEOS_DRIVE_FILE_SYSTEM_OPERATION_OBSERVER_H_
 #define CHROME_BROWSER_CHROMEOS_DRIVE_FILE_SYSTEM_OPERATION_OBSERVER_H_
 
 namespace base {
 class FilePath;
 }
 
 namespace drive {
 namespace file_system {
 
 // Passes notifications from Drive operations back to the file system.
 class OperationObserver {
  public:
   // Sent when a content of a directory has been changed.
   // |directory_path| is a virtual directory path representing the
   // changed directory.
   virtual void OnDirectoryChangedByOperation(
       const base::FilePath& directory_path) = 0;
 
   // Sent when a cache file is modified and upload is needed.
   virtual void OnCacheFileUploadNeededByOperation(
       const std::string& local_id) = 0;
+
+  // Sent when metadata entry is removed and sync is needed.
+  virtual void OnEntryRemovedByOperation(const std::string& local_id) {}
 };
 
 }  // namespace file_system
 }  // namespace drive
 
 #endif  // CHROME_BROWSER_CHROMEOS_DRIVE_FILE_SYSTEM_OPERATION_OBSERVER_H_