Set device scale factor in CompositorFrame and scale frame size in WS.

ui/display/screen_base.cc

Index: ui/display/screen_base.cc
diff --git a/ui/display/screen_base.cc b/ui/display/screen_base.cc
index b3abc48bbbc00622422f804ef2e03ca7e16e95a3..21c8c270f2c21cbf3d29c3f9ef696dceb51e5fd3 100644
--- a/ui/display/screen_base.cc
+++ b/ui/display/screen_base.cc
@@ -39,6 +39,8 @@ Display ScreenBase::GetPrimaryDisplay() const {
 }
 
 Display ScreenBase::GetDisplayNearestWindow(gfx::NativeView view) const {
+  // TODO(riajiang): Implement this for multi-displays either here or in
+  // ScreenMus.
   NOTIMPLEMENTED();
   return GetPrimaryDisplay();
 }