Make DesktopWindowTreeHostX11::ShouldWindowContentsBeTransparent() relies on argb visual flag

ui/views/test/widget_test.h

Index: ui/views/test/widget_test.h
diff --git a/ui/views/test/widget_test.h b/ui/views/test/widget_test.h
index 78392d1a28f3423cb59c45e3d558d2437f1f842a..fe04891ec8648d1d735c5df4fd84a656257d21b3 100644
--- a/ui/views/test/widget_test.h
+++ b/ui/views/test/widget_test.h
@@ -89,6 +89,9 @@ class WidgetTest : public ViewsTestBase {
   static ui::internal::InputMethodDelegate* GetInputMethodDelegateForWidget(
       Widget* widget);
 
+  // Return true if |window| is transparent according to the native platform.
+  static bool IsNativeWindowTransparent(gfx::NativeWindow window);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(WidgetTest);
 };