layout_thread: Note in the debug message whether nodes require dirtying.

components/layout_thread/lib.rs

@@ -1091,7 +1091,7 @@ impl LayoutThread {
         }
 
         let restyles = document.drain_pending_restyles();
-        debug!("Draining restyles: {}", restyles.len());
+        debug!("Draining restyles: {} (needs dirtying? {:?})", restyles.len(), needs_dirtying);
         if !needs_dirtying {
             for (el, restyle) in restyles {
                 // Propagate the descendant bit up the ancestors. Do this before