ash/mash: Fix painting of status-tray bubble.

ui/views/mus/native_widget_mus.cc

Index: ui/views/mus/native_widget_mus.cc
diff --git a/ui/views/mus/native_widget_mus.cc b/ui/views/mus/native_widget_mus.cc
index c501c6e6b843dd4bb60e8ccbbba3b23f4d0526f3..2e98b9cd579553b9bb11cc3d646a709b4b3fadff 100644
--- a/ui/views/mus/native_widget_mus.cc
+++ b/ui/views/mus/native_widget_mus.cc
@@ -472,11 +472,11 @@ Widget* NativeWidgetMus::GetTopLevelWidget() {
 }
 
 const ui::Compositor* NativeWidgetMus::GetCompositor() const {
-  return window_tree_host_->window()->layer()->GetCompositor();
+  return window_tree_host_->compositor();
 }
 
 const ui::Layer* NativeWidgetMus::GetLayer() const {
-  return window_tree_host_ ? window_tree_host_->window()->layer() : nullptr;
+  return content_ ? content_->layer() : nullptr;
 }
 
 void NativeWidgetMus::ReorderNativeViews() {