drive: Return cancel closure from FileSystem::GetFileContent

chrome/browser/chromeos/drive/dummy_file_system.cc

+// Copyright 2014 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.
+
+#include "chrome/browser/chromeos/drive/dummy_file_system.h"
+
+namespace drive {
+
+base::Closure DummyFileSystem::GetFileContent(
+      const base::FilePath& file_path,
+      const GetFileContentInitializedCallback& initialized_callback,
+      const google_apis::GetContentCallback& get_content_callback,
+      const FileOperationCallback& completion_callback) {
+  return base::Bind(&base::DoNothing);
+}
+
+}  // namespace drive