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

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 11f105d675ea49025ae95c3d1f6582d3a46404da..dfe4cbfb01a44c9ccbfdcbdedd622fd0b78192d5 100644
--- a/services/ui/ws/platform_display_default.cc
+++ b/services/ui/ws/platform_display_default.cc
@@ -34,7 +34,10 @@ PlatformDisplayDefault::PlatformDisplayDefault(
 #if !defined(OS_ANDROID)
       cursor_loader_(ui::CursorLoader::Create()),
 #endif
-      frame_generator_(new FrameGenerator(this, init_params.root_window)),
+      frame_generator_(
+          new FrameGenerator(this,
+                             init_params.root_window,
+                             init_params.metrics.device_scale_factor)),
       metrics_(init_params.metrics) {
 }
 
@@ -141,6 +144,7 @@ bool PlatformDisplayDefault::UpdateViewportMetrics(
   }
 
   metrics_ = metrics;
+  frame_generator_->UpdateDeviceScaleFactor(metrics_.device_scale_factor);
   return true;
 }