Extend Iterable instead of implementing it.

utils/apidoc/mdn/extract.dart

 import 'dart:html';
 import 'dart:json';
 
 // Workaround for HTML lib missing feature.
 Range newRange() {
   return document.createRange();
 }
 
 // Temporary range object to optimize performance computing client rects
 // from text nodes.
@@ skipping 457 matching lines @@
   }
 
   static Node _leftMostDescendent(Node n) {
     while (n.nodes.length > 0) {
       n = n.nodes.first;
     }
     return n;
   }
 }
 
-class PostOrderTraversal implements Iterable<Node> {
+class PostOrderTraversal extends Iterable<Node> {
   final Node _node;
   PostOrderTraversal(this._node);
 
   Iterator<Node> iterator() => new PostOrderTraversalIterator(_node);
 }
 
 /**
  * Estimate what content represents the first line of text within the [section]
  * range returning null if there isn't a plausible first line of text that
  * contains the string [prop].  We measure the actual rendered client rectangle
@@ skipping 816 matching lines @@
 }
 
 void documentLoaded(event) {
   // Load the database of expected methods and properties with an HttpRequest.
   new HttpRequest.get('${window.location}.json', (req) {
     data = JSON.parse(req.responseText);
     dbEntry = {'members': [], 'srcUrl': pageUrl};
     run();
   });
 }