Replace script thread root browsing context by a collection of documents.

components/script/dom/nodelist.rs

@@ -97,6 +97,13 @@ impl NodeList {
             panic!("called as_simple_list() on a children node list")
         }
     }
+
+    pub fn iter(&self) -> NodeListIterator {
+        NodeListIterator {
+            nodes: self,
+            offset: 0,
+        }
+    }
 }
 
 #[derive(JSTraceable, HeapSizeOf)]
@@ -277,3 +284,18 @@ impl ChildrenList {
         self.last_index.set(0u32);
     }
 }
+
+pub struct NodeListIterator<'a> {
+    nodes: &'a NodeList,
+    offset: u32,
+}
+
+impl<'a> Iterator for NodeListIterator<'a> {
+    type Item = Root<Node>;
+
+    fn next(&mut self) -> Option<Root<Node>> {
+        let result = self.nodes.Item(self.offset);
+        self.offset = self.offset + 1;
+        result
+    }
+}