Fix black screen when switching primary display without bounds change

ui/ozone/platform/drm/gpu/mock_scanout_buffer.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_MOCK_SCANOUT_BUFFER_H_
 #define UI_OZONE_PLATFORM_DRM_GPU_MOCK_SCANOUT_BUFFER_H_
 
 #include <drm_fourcc.h>
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "ui/ozone/platform/drm/gpu/scanout_buffer.h"
 
 namespace ui {
 
 class MockScanoutBuffer : public ScanoutBuffer {
  public:
   MockScanoutBuffer(const gfx::Size& size,
                     uint32_t format = DRM_FORMAT_XRGB8888);
 
   // ScanoutBuffer:
   uint32_t GetFramebufferId() const override;
   uint32_t GetHandle() const override;
   gfx::Size GetSize() const override;
   uint32_t GetFramebufferPixelFormat() const override;
+  const DrmDevice* GetDrmDevice() const override;
   bool RequiresGlFinish() const override;
 
  private:
   ~MockScanoutBuffer() override;
 
   gfx::Size size_;
   uint32_t format_;
 
   DISALLOW_COPY_AND_ASSIGN(MockScanoutBuffer);
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PLATFORM_DRM_GPU_MOCK_SCANOUT_BUFFER_H_