backport of r60185.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_9_0_BRANCH@60244 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/graphicc.cpp

@@ -1738,6 +1738,9 @@ wxGraphicsContext * wxCairoRenderer::CreateContextFromNativeWindow( void * windo
 
 wxGraphicsContext * wxCairoRenderer::CreateMeasuringContext()
 {
+#ifdef __WXGTK__
+    return CreateContextFromNativeWindow(gdk_get_default_root_window());
+#endif
     return NULL;
     // TODO
 }