ozone: Fix use_drm_atomic=true compile error.

ui/ozone/platform/drm/gpu/hardware_display_plane_atomic.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_HARDWARE_DISPLAY_PLANE_ATOMIC_H_
 #define UI_OZONE_PLATFORM_DRM_GPU_HARDWARE_DISPLAY_PLANE_ATOMIC_H_
 
 #include "ui/ozone/platform/drm/gpu/hardware_display_plane.h"
 
 #include <stdint.h>
 #include <xf86drmMode.h>
 
+namespace gfx {
+class Rect;
+}  // namespace gfx
+
 namespace ui {
 
 class CrtcController;
 class DrmDevice;
 
 class HardwareDisplayPlaneAtomic : public HardwareDisplayPlane {
  public:
   HardwareDisplayPlaneAtomic(uint32_t plane_id, uint32_t possible_crtcs);
   ~HardwareDisplayPlaneAtomic() override;
 
@@ skipping 28 matching lines @@
   Property src_x_prop_;
   Property src_y_prop_;
   Property src_w_prop_;
   Property src_h_prop_;
   CrtcController* crtc_ = nullptr;
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PLATFORM_DRM_GPU_HARDWARE_DISPLAY_PLANE_ATOMIC_H_