drive: Return cancel closure from FileSystem::GetFileContent

chrome/browser/chromeos/drive/file_system.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_H_
 #define CHROME_BROWSER_CHROMEOS_DRIVE_FILE_SYSTEM_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 109 matching lines @@
                             int64 length,
                             const FileOperationCallback& callback) OVERRIDE;
   virtual void Pin(const base::FilePath& file_path,
                    const FileOperationCallback& callback) OVERRIDE;
   virtual void Unpin(const base::FilePath& file_path,
                      const FileOperationCallback& callback) OVERRIDE;
   virtual void GetFile(const base::FilePath& file_path,
                              const GetFileCallback& callback) OVERRIDE;
   virtual void GetFileForSaving(const base::FilePath& file_path,
                                       const GetFileCallback& callback) OVERRIDE;
-  virtual void GetFileContent(
+  virtual base::Closure GetFileContent(
       const base::FilePath& file_path,
       const GetFileContentInitializedCallback& initialized_callback,
       const google_apis::GetContentCallback& get_content_callback,
       const FileOperationCallback& completion_callback) OVERRIDE;
   virtual void GetResourceEntry(
       const base::FilePath& file_path,
       const GetResourceEntryCallback& callback) OVERRIDE;
   virtual void ReadDirectory(
       const base::FilePath& directory_path,
       const ReadDirectoryCallback& callback) OVERRIDE;
@@ skipping 158 matching lines @@
   // 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<FileSystem> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(FileSystem);
 };
 
 }  // namespace drive
 
 #endif  // CHROME_BROWSER_CHROMEOS_DRIVE_FILE_SYSTEM_H_