Handle modified displays in mustash.

services/ui/ws/frame_generator.cc

Index: services/ui/ws/frame_generator.cc
diff --git a/services/ui/ws/frame_generator.cc b/services/ui/ws/frame_generator.cc
index 825a90a2a0c2b32c3aaa67bd0739c303ca7fd49f..ff03b16adc9a5b9b6d47209ba0ccc101428fcc71 100644
--- a/services/ui/ws/frame_generator.cc
+++ b/services/ui/ws/frame_generator.cc
@@ -82,8 +82,7 @@ void FrameGenerator::Draw() {
   if (!delegate_->GetRootWindow()->visible())
     return;
 
-  const ViewportMetrics& metrics = delegate_->GetViewportMetrics();
-  const gfx::Rect output_rect(metrics.pixel_size);
+  const gfx::Rect output_rect(delegate_->GetViewportMetrics().pixel_size);
   dirty_rect_.Intersect(output_rect);
   // TODO(fsamuel): We should add a trace for generating a top level frame.
   cc::CompositorFrame frame(GenerateCompositorFrame(output_rect));