auto merge of #646 : kmcallister/servo/incremental-layout, r=metajack

This is a first attempt at incremental layout.  When recomputing styles, we compare old and new CSS properties to determine which layout steps can be skipped.

Since I'm new to Servo I'm not sure that my code matches the idioms of the project.  Please don't hold back with review comments :)

1 files changed, 6 insertions, 4 deletions

diff --git a/src/components/script/dom/node.rs b/src/components/script/dom/node.rs
index d9ee80edaa1..edd108e6881 100644
--- a/src/components/script/dom/node.rs
+++ b/src/components/script/dom/node.rs
@@ -264,6 +264,11 @@ impl<'self, View> AbstractNode<View> {
         self.with_base(|b| b.next_sibling)
     }
 
+    /// Is this node a root?
+    pub fn is_root(self) -> bool {
+        self.parent_node().is_none()
+    }
+
     //
     // Downcasting borrows
     //
@@ -415,10 +420,7 @@ impl<'self, View> AbstractNode<View> {
 impl<View> Iterator<AbstractNode<View>> for AbstractNodeChildrenIterator<View> {
     pub fn next(&mut self) -> Option<AbstractNode<View>> {
         let node = self.current_node;
-        self.current_node = match self.current_node {
-            None => None,
-            Some(node) => node.next_sibling(),
-        };
+        self.current_node = self.current_node.chain(|node| node.next_sibling());
         node
     }
 }