Fix black screen when switching primary display without bounds change

ui/ozone/platform/drm/gpu/drm_buffer.cc

 // 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.
 
 #include "ui/ozone/platform/drm/gpu/drm_buffer.h"
 
 #include <drm_fourcc.h>
 
 #include "base/logging.h"
 #include "third_party/skia/include/core/SkSurface.h"
@@ skipping 88 matching lines @@
 }
 
 uint32_t DrmBuffer::GetHandle() const {
   return handle_;
 }
 
 gfx::Size DrmBuffer::GetSize() const {
   return gfx::Size(surface_->width(), surface_->height());
 }
 
+const DrmDevice* DrmBuffer::GetDrmDevice() const {
+  return drm_.get();
+}
+
 bool DrmBuffer::RequiresGlFinish() const {
   return false;
 }
 
 }  // namespace ui