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

content/browser/compositor/mus_browser_compositor_output_surface.cc

Index: content/browser/compositor/mus_browser_compositor_output_surface.cc
diff --git a/content/browser/compositor/mus_browser_compositor_output_surface.cc b/content/browser/compositor/mus_browser_compositor_output_surface.cc
index ef3f66a41d886a06bf93384a4918676fab673388..a107595de4d60a564a8a943846e9808aa9b632c7 100644
--- a/content/browser/compositor/mus_browser_compositor_output_surface.cc
+++ b/content/browser/compositor/mus_browser_compositor_output_surface.cc
@@ -19,6 +19,7 @@
 #include "ui/aura/mus/window_compositor_frame_sink.h"
 #include "ui/aura/mus/window_port_mus.h"
 #include "ui/aura/window.h"
+#include "ui/display/screen.h"
 
 namespace content {
 
@@ -73,6 +74,9 @@ void MusBrowserCompositorOutputSurface::SwapBuffers(
   const gfx::Rect bounds = ui_window_ ? gfx::Rect(ui_window_->bounds().size())
                                       : gfx::Rect(window_->bounds().size());
   cc::CompositorFrame ui_frame;
+  ui_frame.metadata.device_scale_factor = display::Screen::GetScreen()
+                                              ->GetDisplayNearestWindow(window_)
+                                              .device_scale_factor();
   ui_frame.metadata.latency_info = std::move(frame.latency_info);
   // Reset latency_info to known empty state after moving contents.
   frame.latency_info.clear();