Add a flag use_software_compositing to the Widget::InitParams structure.

ui/views/widget/widget.h

Index: ui/views/widget/widget.h
diff --git a/ui/views/widget/widget.h b/ui/views/widget/widget.h
index 320332bec2461bd309d694e3651eabc7ba38c712..c7c8a93bb93d68ec09e5c4776cd686dd04f456a2 100644
--- a/ui/views/widget/widget.h
+++ b/ui/views/widget/widget.h
@@ -266,6 +266,10 @@ class VIEWS_EXPORT Widget : public internal::NativeWidgetDelegate,
     std::string wm_role_name;
     std::string wm_class_name;
     std::string wm_class_class;
+
+    // If true then the widget uses software compositing. Defaults to false.
+    // Only used on Windows.
+    bool force_software_compositing;
   };
 
   Widget();