chrome: Cleanup class/struct forward declarations

chrome/utility/image_writer/disk_unmounter_mac.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_UTILITY_IMAGE_WRITER_DISK_UNMOUNTER_MAC_H_
 #define CHROME_UTILITY_IMAGE_WRITER_DISK_UNMOUNTER_MAC_H_
 
 #include <CoreFoundation/CoreFoundation.h>
 #include <DiskArbitration/DiskArbitration.h>
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/mac/foundation_util.h"
 #include "base/memory/weak_ptr.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread.h"
 
 namespace image_writer {
 
-class ImageWriter;
-
 // Manages the unmounting of disks through Disk Arbitration.  Disk Arbitration
 // has to be run on a thread with a CFRunLoop.  In the utility process neither
 // the main or IO thread have one by default, so we need to manage a new thread
 // which will explicitly have a CFRunLoop-based message pump.  Note that this
 // class can only handle one unmount operation at a time and calling Unmount
 // again before the continuation returns will cause undefined behavior.
 class DiskUnmounterMac {
  public:
   DiskUnmounterMac();
   ~DiskUnmounterMac();
@@ skipping 34 matching lines @@
   base::ScopedCFTypeRef<DASessionRef> session_;
 
   // Thread is last to ensure it is stopped before the data members are
   // destroyed.
   base::Thread cf_thread_;
 };
 
 }  // namespace image_writer
 
 #endif  // CHROME_UTILITY_IMAGE_WRITER_DISK_UNMOUNTER_MAC_H_