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/slider.h

@@ -80,6 +80,9 @@ public:
     virtual int GetSelStart() const { return GetMax(); }
     virtual void SetSelection(int WXUNUSED(min), int WXUNUSED(max)) { }
 
+
+    virtual bool CanApplyParentThemeBackground() const { return true; }
+
 private:
     DECLARE_NO_COPY_CLASS(wxSliderBase)
 };