chrome: Cleanup class/struct forward declarations

chrome/browser/chromeos/file_manager/volume_manager.h

 // 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_FILE_MANAGER_VOLUME_MANAGER_H_
 #define CHROME_BROWSER_CHROMEOS_FILE_MANAGER_VOLUME_MANAGER_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 21 matching lines @@
 namespace chromeos {
 class PowerManagerClient;
 }  // namespace chromeos
 
 namespace content {
 class BrowserContext;
 }  // namespace content
 
 namespace file_manager {
 
-class MountedDiskMonitor;
 class SnapshotManager;
 class VolumeManagerObserver;
 
 // Identifiers for volume types managed by Chrome OS file manager.
 enum VolumeType {
   VOLUME_TYPE_TESTING = -1,  // Used only in tests.
   VOLUME_TYPE_GOOGLE_DRIVE = 0,
   VOLUME_TYPE_DOWNLOADS_DIRECTORY,
   VOLUME_TYPE_REMOVABLE_DISK_PARTITION,
   VOLUME_TYPE_MOUNTED_ARCHIVE_FILE,
@@ skipping 282 matching lines @@
 
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate its weak pointers before any other members are destroyed.
   base::WeakPtrFactory<VolumeManager> weak_ptr_factory_;
   DISALLOW_COPY_AND_ASSIGN(VolumeManager);
 };
 
 }  // namespace file_manager
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILE_MANAGER_VOLUME_MANAGER_H_