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/vlbox.h

@@ -189,6 +189,8 @@ public:
     void SetSelectionBackground(const wxColour& col);
 
 
+    virtual bool CanApplyParentThemeBackground() const { return false; }
+    
 protected:
     // the derived class must implement this function to actually draw the item
     // with the given index on the provided DC