Pass device scale factor from display to ws.

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 4ab9589b8636c8dfeb4fd9c71a78377224b46d89..d1d6b6b29562455ddb6bcf24d216b136bbfb5c76 100644
--- a/services/ui/ws/frame_generator.cc
+++ b/services/ui/ws/frame_generator.cc
@@ -84,7 +84,7 @@ void FrameGenerator::Draw() {
     return;
 
   const ViewportMetrics& metrics = delegate_->GetViewportMetrics();
-  const gfx::Rect output_rect(metrics.bounds.size());
+  const gfx::Rect output_rect(metrics.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));