ui: Cleanup class/struct forward declarations

ui/display/chromeos/apply_content_protection_task.h

 // Copyright 2015 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 UI_DISPLAY_CHROMEOS_APPLY_CONTENT_PROTECTION_TASK_H_
 #define UI_DISPLAY_CHROMEOS_APPLY_CONTENT_PROTECTION_TASK_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <map>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "ui/display/chromeos/display_configurator.h"
 
 namespace ui {
 
 class DisplayLayoutManager;
-class DisplaySnapshot;
 class NativeDisplayDelegate;
 
 // In order to apply content protection the task executes in the following
 // manner:
 // 1) Run()
 //   a) Query NativeDisplayDelegate for HDCP state on capable displays
 //   b) OnHDCPStateUpdate() called for each display as response to (a)
 // 2) ApplyProtections()
 //   a) Compute preferred HDCP state for capable displays
 //   b) Call into NativeDisplayDelegate to set HDCP state on capable displays
@@ skipping 48 matching lines @@
   size_t pending_requests_;
 
   base::WeakPtrFactory<ApplyContentProtectionTask> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ApplyContentProtectionTask);
 };
 
 }  // namespace ui
 
 #endif  // UI_DISPLAY_CHROMEOS_APPLY_CONTENT_PROTECTION_TASK_H_