layout: Keep track of whether we've deferred the painting of the document due to

a script query.

This will, rather unfortunately, mean that we might repaint two times if we've
deferred a paint, then get an out-of-band reflow. Still seemed better than not
suppressing paints at all.

Fixes #13131

components/style/dom.rs

@@ -179,6 +179,9 @@ pub trait TDocument : Sized + Copy + Clone {
 
     fn drain_modified_elements(&self) -> Vec<(Self::ConcreteElement,
                                               <Self::ConcreteElement as ElementExt>::Snapshot)>;
+
+    fn needs_paint_from_layout(&self);
+    fn will_paint(&self);
 }
 
 pub trait PresentationalHintsSynthetizer {