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

ui/views/mus/native_widget_mus_unittest.cc

Index: ui/views/mus/native_widget_mus_unittest.cc
diff --git a/ui/views/mus/native_widget_mus_unittest.cc b/ui/views/mus/native_widget_mus_unittest.cc
index a2ff4b065e8e1677b19def6ba2520a34a8a6b8a6..8dcebbcd8015e20124e8ab3bb7c1dd944a37160b 100644
--- a/ui/views/mus/native_widget_mus_unittest.cc
+++ b/ui/views/mus/native_widget_mus_unittest.cc
@@ -12,6 +12,7 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkColor.h"
+#include "ui/aura/window.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/gfx/skia_util.h"
@@ -124,5 +125,13 @@ TEST_F(NativeWidgetMusTest, ChangeAppIcon) {
   EXPECT_TRUE(gfx::BitmapsAreEqual(bitmap2, icon));
 }
 
+TEST_F(NativeWidgetMusTest, ValidLayerTree) {
+  scoped_ptr<Widget> widget(CreateWidget(nullptr));
+  View* content = new View;
+  content->SetPaintToLayer(true);
+  widget->GetContentsView()->AddChildView(content);
+  EXPECT_TRUE(widget->GetNativeWindow()->layer()->Contains(content->layer()));
+}
+
 }  // namespace
 }  // namespace views