Add a missing include in fake_disk_mount_manager.cc.

chrome/browser/chromeos/file_manager/fake_disk_mount_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_FAKE_DISK_MOUNT_MANAGER_H_
 #define CHROME_BROWSER_CHROMEOS_FILE_MANAGER_FAKE_DISK_MOUNT_MANAGER_H_
 
 #include <queue>
 #include <string>
 #include <vector>
 
+#include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "chromeos/dbus/cros_disks_client.h"
 #include "chromeos/disks/disk_mount_manager.h"
 
 namespace file_manager {
 
 class FakeDiskMountManager : public chromeos::disks::DiskMountManager {
  public:
@@ skipping 74 matching lines @@
 
   std::vector<MountRequest> mount_requests_;
   std::vector<UnmountRequest> unmount_requests_;
 
   DISALLOW_COPY_AND_ASSIGN(FakeDiskMountManager);
 };
 
 }  // namespace file_manager
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILE_MANAGER_FAKE_DISK_MOUNT_MANAGER_H_