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 c807ae8a71b52e9d2d53f1bf9987148c0fde1b0c..6a14cca1cf13455235d18f2115b70bd0ef379998 100644
--- a/services/ui/ws/platform_display_default.cc
+++ b/services/ui/ws/platform_display_default.cc
@@ -125,6 +125,10 @@ gfx::Rect PlatformDisplayDefault::GetBounds() const {
   return metrics_.bounds;
 }
 
+FrameGenerator* PlatformDisplayDefault::GetFrameGenerator() {
+  return frame_generator_.get();
+}
+
 void PlatformDisplayDefault::OnGpuChannelEstablished(
     scoped_refptr<gpu::GpuChannelHost> channel) {
   frame_generator_->OnGpuChannelEstablished(channel);