Fix black screen when switching primary display without bounds change

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

Index: ui/ozone/platform/drm/gpu/mock_scanout_buffer.cc
diff --git a/ui/ozone/platform/drm/gpu/mock_scanout_buffer.cc b/ui/ozone/platform/drm/gpu/mock_scanout_buffer.cc
index 60fbf5df3decb2401951385308952e844e177e73..d372f8e9654eb2fa339168e0c34967c35813a97d 100644
--- a/ui/ozone/platform/drm/gpu/mock_scanout_buffer.cc
+++ b/ui/ozone/platform/drm/gpu/mock_scanout_buffer.cc
@@ -27,6 +27,10 @@ uint32_t MockScanoutBuffer::GetFramebufferPixelFormat() const {
   return format_;
 }
 
+const DrmDevice* MockScanoutBuffer::GetDrmDevice() const {
+  return nullptr;
+}
+
 bool MockScanoutBuffer::RequiresGlFinish() const {
   return false;
 }