Switch DRM platform to using a separate thread

ui/ozone/platform/drm/gpu/drm_window.h

 // Copyright 2014 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_WINDOW_H_
 #define UI_OZONE_PLATFORM_DRM_GPU_DRM_WINDOW_H_
 
 #include <vector>
 
 #include "base/timer/timer.h"
@@ skipping 10 matching lines @@
 class SkBitmap;
 
 namespace gfx {
 class Point;
 class Rect;
 }  // namespace gfx
 
 namespace ui {
 
 class DrmBuffer;
+class DrmDevice;
 class DrmDeviceManager;
 class HardwareDisplayController;
 struct OverlayCheck_Params;
 class ScanoutBufferGenerator;
 class ScreenManager;
 
 // The GPU object representing a window.
 //
 // The main purpose of this object is to associate drawing surfaces with
 // displays. A surface created with the same id as the window (from
@@ skipping 90 matching lines @@
   OverlayPlaneList last_submitted_planes_;
 
   bool force_buffer_reallocation_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(DrmWindow);
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PLATFORM_DRM_GPU_DRM_WINDOW_H_