Added CanApplyParentThemeBackground and use it in wxMSW's

wxNotebook::ApplyThemeBackground.  It's in the common base classes so
that someday it's usage can expand to the other platforms as well.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@26085 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/checkbox.h

@@ -106,6 +106,8 @@ public:
         return HasFlag(wxCHK_ALLOW_3RD_STATE_FOR_USER);
     }
 
+    virtual bool CanApplyParentThemeBackground() const { return true; }
+
 protected:
     virtual void DoSet3StateValue(wxCheckBoxState WXUNUSED(state)) { wxFAIL; }