ui: Cleanup class/struct forward declarations

ui/ozone/platform/drm/gpu/drm_overlay_validator.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_OZONE_PLATFORM_DRM_GPU_DRM_OVERLAY_VALIDATOR_H_
 #define UI_OZONE_PLATFORM_DRM_GPU_DRM_OVERLAY_VALIDATOR_H_
 
 #include "base/containers/mru_cache.h"
 #include "ui/ozone/platform/drm/gpu/overlay_plane.h"
 
 namespace ui {
 
-class DrmDevice;
 class DrmWindow;
-class HardwareDisplayController;
 class ScanoutBufferGenerator;
 struct OverlayCheck_Params;
 
 class DrmOverlayValidator {
  public:
   DrmOverlayValidator(DrmWindow* window,
                       ScanoutBufferGenerator* buffer_generator);
   ~DrmOverlayValidator();
 
   // Tests if configurations |params| are compatible with |window_| and finds
@@ skipping 41 matching lines @@
 
   // List of all configurations which have been validated.
   base::MRUCache<OverlayPlaneList, OverlayHintsList> overlay_hints_cache_;
 
   DISALLOW_COPY_AND_ASSIGN(DrmOverlayValidator);
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PLATFORM_DRM_GPU_DRM_OVERLAY_VALIDATOR_H_