google_apis: Fix use-after-free of URLFetcher* in ResponseWriter

google_apis/drive/base_requests.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.
 //
 // This file provides base classes used to issue HTTP requests for Google
 // APIs.
 
 #ifndef GOOGLE_APIS_DRIVE_BASE_REQUESTS_H_
 #define GOOGLE_APIS_DRIVE_BASE_REQUESTS_H_
 
@@ skipping 84 matching lines @@
   // If file_path is not empty, the response will be saved with file_writer_,
   // otherwise it will be saved to data_.
   ResponseWriter(net::URLFetcher* url_fetcher,
                  base::SequencedTaskRunner* file_task_runner,
                  const base::FilePath& file_path,
                  const GetContentCallback& get_content_callback);
   virtual ~ResponseWriter();
 
   const std::string& data() const { return data_; }
 
+  // Detaches this object from url_fetcher_.
+  void Detach();
+
   // Disowns the output file.
   void DisownFile();
 
   // URLFetcherResponseWriter overrides:
   virtual int Initialize(const net::CompletionCallback& callback) OVERRIDE;
   virtual int Write(net::IOBuffer* buffer,
                     int num_bytes,
                     const net::CompletionCallback& callback) OVERRIDE;
   virtual int Finish(const net::CompletionCallback& callback) OVERRIDE;
 
@@ skipping 412 matching lines @@
   const ProgressCallback progress_callback_;
   const GURL download_url_;
   const base::FilePath output_file_path_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadFileRequestBase);
 };
 
 }  // namespace google_apis
 
 #endif  // GOOGLE_APIS_DRIVE_BASE_REQUESTS_H_