Filter non-element / non-text nodes in LayoutIterator.

components/script/layout_wrapper.rs

@@ -734,9 +734,14 @@ impl<'ln> NodeInfo for ServoThreadSafeLayoutNode<'ln> {
     fn is_element(&self) -> bool {
         if let Some(LayoutNodeType::Element(_)) = self.type_id() { true } else { false }
     }
+
     fn is_text_node(&self) -> bool {
         if let Some(LayoutNodeType::Text) = self.type_id() { true } else { false }
     }
+
+    fn needs_layout(&self) -> bool {
+        self.pseudo != PseudoElementType::Normal || self.is_element() || self.is_text_node()
+    }
 }
 
 impl<'ln> ThreadSafeLayoutNode for ServoThreadSafeLayoutNode<'ln> {

components/style/dom.rs

@@ -71,13 +71,22 @@ pub trait TRestyleDamage : Debug + PartialEq + BitOr<Output=Self> + Copy {
 pub trait NodeInfo {
     fn is_element(&self) -> bool;
     fn is_text_node(&self) -> bool;
+
+    // Comments, doctypes, etc are ignored by layout algorithms.
+    fn needs_layout(&self) -> bool { self.is_element() || self.is_text_node() }
 }
 
 pub struct LayoutIterator<T>(pub T);
 impl<T, I> Iterator for LayoutIterator<T> where T: Iterator<Item=I>, I: NodeInfo {
     type Item = I;
     fn next(&mut self) -> Option<I> {
-        self.0.next()
+        loop {
+            // Filter out nodes that layout should ignore.
+            let n = self.0.next();
+            if n.is_none() || n.as_ref().unwrap().needs_layout() {
+                return n
+            }
+        }
     }
 }