Scale client area, hit test mask and bounds by device_scale_factor.

services/ui/demo/mus_demo.h

Index: services/ui/demo/mus_demo.h
diff --git a/services/ui/demo/mus_demo.h b/services/ui/demo/mus_demo.h
index 912519a19058e9c2f0db56bcccad4b2ff5be7c7a..941b2387be42874fd4287f2006f32215ba625cf4 100644
--- a/services/ui/demo/mus_demo.h
+++ b/services/ui/demo/mus_demo.h
@@ -18,6 +18,7 @@
 #include "services/ui/public/cpp/window_manager_delegate.h"
 #include "services/ui/public/cpp/window_tree_client_delegate.h"
 #include "third_party/skia/include/core/SkBitmap.h"
+#include "ui/display/screen_base.h"
 
 namespace ui {
 class BitmapUploader;
@@ -78,6 +79,9 @@ class MusDemo : public service_manager::Service,
   std::unique_ptr<WindowTreeClient> window_tree_client_;
   std::unique_ptr<GpuService> gpu_service_;
 
+  // Dummy screen required to be the screen instance.
+  std::unique_ptr<display::ScreenBase> screen_;
+
   // Used to send frames to mus.
   std::unique_ptr<BitmapUploader> uploader_;