drive: Return cancel closure from FileSystem::GetFileContent

chrome/browser/chromeos/drive/file_system/download_operation.h

 // Copyright 2013 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_DOWNLOAD_OPERATION_H_
 #define CHROME_BROWSER_CHROMEOS_DRIVE_FILE_SYSTEM_DOWNLOAD_OPERATION_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/chromeos/drive/file_errors.h"
@@ skipping 29 matching lines @@
  public:
   DownloadOperation(base::SequencedTaskRunner* blocking_task_runner,
                     OperationObserver* observer,
                     JobScheduler* scheduler,
                     internal::ResourceMetadata* metadata,
                     internal::FileCache* cache,
                     const base::FilePath& temporary_file_directory);
   ~DownloadOperation();
 
   // Ensures that the file content specified by |local_id| is locally
-  // downloaded.
+  // downloaded and returns a closure to cancel the task.
   // For hosted documents, this method may create a JSON file representing the
   // file.
   // For regular files, if the locally cached file is found, returns it.
   // If not found, start to download the file from the server.
   // When a JSON file is created, the cache file is found or downloading is
   // being started, |initialized_callback| is called with |local_file|
   // for JSON file or the cache file, or with |cancel_download_closure| for
   // downloading.
   // During the downloading |get_content_callback| will be called periodically
   // with the downloaded content.
   // Upon completion or an error is found, |completion_callback| will be called.
   // |initialized_callback| and |get_content_callback| can be null if not
   // needed.
   // |completion_callback| must not be null.
-  void EnsureFileDownloadedByLocalId(
+  base::Closure EnsureFileDownloadedByLocalId(
       const std::string& local_id,
       const ClientContext& context,
       const GetFileContentInitializedCallback& initialized_callback,
       const google_apis::GetContentCallback& get_content_callback,
       const GetFileCallback& completion_callback);
 
   // Does the same thing as EnsureFileDownloadedByLocalId for the file
   // specified by |file_path|.
-  void EnsureFileDownloadedByPath(
+  base::Closure EnsureFileDownloadedByPath(
       const base::FilePath& file_path,
       const ClientContext& context,
       const GetFileContentInitializedCallback& initialized_callback,
       const google_apis::GetContentCallback& get_content_callback,
       const GetFileCallback& completion_callback);
 
  private:
   // Parameters for EnsureFileDownloaded.
   class DownloadParams;
 
@@ skipping 43 matching lines @@
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate its weak pointers before any other members are destroyed.
   base::WeakPtrFactory<DownloadOperation> weak_ptr_factory_;
   DISALLOW_COPY_AND_ASSIGN(DownloadOperation);
 };
 
 }  // namespace file_system
 }  // namespace drive
 
 #endif  // CHROME_BROWSER_CHROMEOS_DRIVE_FILE_SYSTEM_DOWNLOAD_OPERATION_H_