Add wr-debug option.

components/servo/lib.rs

@@ -150,6 +150,7 @@ impl<Window> Browser<Window> where Window: WindowMethods + 'static {
                         enable_aa: opts.enable_text_antialiasing,
                         enable_msaa: opts.use_msaa,
                         enable_profiler: opts.webrender_stats,
+                        debug: opts.webrender_debug,
                     });
                 (Some(webrender), Some(webrender_sender))
             } else {