Deflake ImageWriterUtilityClient browsertest and clients

chrome/browser/extensions/api/image_writer_private/image_writer_utility_client.h

 // 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_API_IMAGE_WRITER_PRIVATE_IMAGE_WRITER_UTILITY_CLIENT_H_
 #define CHROME_BROWSER_EXTENSIONS_API_IMAGE_WRITER_PRIVATE_IMAGE_WRITER_UTILITY_CLIENT_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #include "chrome/common/extensions/removable_storage_writer.mojom.h"
 #include "content/public/browser/utility_process_mojo_client.h"
 
-// Writes a disk image to a device inside the utility process.
+// Writes a disk image to a device inside the utility process. This
+// class lives on the FILE thread.
 class ImageWriterUtilityClient
     : public base::RefCountedThreadSafe<ImageWriterUtilityClient> {
  public:
   typedef base::Callback<void()> CancelCallback;
   typedef base::Callback<void()> SuccessCallback;
   typedef base::Callback<void(int64_t)> ProgressCallback;
   typedef base::Callback<void(const std::string&)> ErrorCallback;
 
   ImageWriterUtilityClient();
 
@@ skipping 42 matching lines @@
   void OperationProgress(int64_t progress);
   void OperationSucceeded();
   void OperationFailed(const std::string& error);
 
   void ResetRequest();
 
   ProgressCallback progress_callback_;
   SuccessCallback success_callback_;
   ErrorCallback error_callback_;
 
-  const scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
-
   std::unique_ptr<content::UtilityProcessMojoClient<
       extensions::mojom::RemovableStorageWriter>>
       utility_process_mojo_client_;
 
   std::unique_ptr<RemovableStorageWriterClientImpl>
       removable_storage_writer_client_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageWriterUtilityClient);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_IMAGE_WRITER_PRIVATE_IMAGE_WRITER_UTILITY_CLIENT_H_