Resubmit of 149313003: Significantly cleans up the ImageWriter Operation class and subclasses.

chrome/browser/extensions/api/image_writer_private/operation_mac.cc

 // 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.
 
 #include "chrome/browser/extensions/api/image_writer_private/error_messages.h"
 #include "chrome/browser/extensions/api/image_writer_private/operation.h"
 
 namespace extensions {
 namespace image_writer {
 
-void Operation::WriteStart() {
+void Operation::Write(const base::Closure& continuation) {
   Error(error::kUnsupportedOperation);
 }
 
-void Operation::VerifyWriteStart() {
+void Operation::VerifyWrite(const base::Closure& continuation) {
   Error(error::kUnsupportedOperation);
 }
 
 } // namespace image_writer
 } // namespace extensions