Explicitly implementing some DOM iterable APIs for performance

tests/html/node_test.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library NodeTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 import 'dart:svg' as svg;
 
@@ skipping 100 matching lines @@
       expect(node.nodes[7], isInputElement);
       expect(node.nodes[8], isComment);
     });
   });
 
   group('nodes', () {
     test('is a NodeList', () {
       expect(makeNodeWithChildren().nodes, isNodeList);
     });
 
+    test('indexer', () {
+      var node = new DivElement();
+      expect(() {
+        node.nodes[0];
+      }, throwsRangeError);
+
+      expect(() {
+        node.nodes[-1];
+      }, throwsRangeError);
+    });
+
     test('first', () {
       var node = makeNodeWithChildren();
       expect(node.nodes.first, isText);
 
       node = new DivElement();
       expect(() {
         node = node.nodes.first;
       }, throwsStateError);
     });
 
@@ skipping 226 matching lines @@
     });
 
     test('TreeWalker', () {
       var root = makeNodeWithChildren();
       var treeWalker = new TreeWalker(root, NodeFilter.SHOW_COMMENT);
       expect(treeWalker.nextNode(), isComment);
       expect(treeWalker.nextNode(), isNull);
     });
   });
 }