Convert mustash use surface references.

services/ui/ws/platform_display_default.cc

Index: services/ui/ws/platform_display_default.cc
diff --git a/services/ui/ws/platform_display_default.cc b/services/ui/ws/platform_display_default.cc
index 9492e85cb8fdd0d5da5d16a0032c53b18d6fbefd..c1380535b5fe98453df1a9fa3906eb50d917b4e0 100644
--- a/services/ui/ws/platform_display_default.cc
+++ b/services/ui/ws/platform_display_default.cc
@@ -130,6 +130,10 @@ bool PlatformDisplayDefault::IsPrimaryDisplay() const {
          display_id_;
 }
 
+FrameGenerator* PlatformDisplayDefault::GetFrameGenerator() {
+  return frame_generator_.get();
+}
+
 void PlatformDisplayDefault::OnGpuChannelEstablished(
     scoped_refptr<gpu::GpuChannelHost> channel) {
   frame_generator_->OnGpuChannelEstablished(channel);