Properly exposing NodeIterator and TreeWalker.

tests/html/node_test.dart

Index: tests/html/node_test.dart
diff --git a/tests/html/node_test.dart b/tests/html/node_test.dart
index ad4911e250bf742aa6323cfe27db485c2a382b25..c8a009cdc3a535be01311d3d97aa03830ca7ba99 100644
--- a/tests/html/node_test.dart
+++ b/tests/html/node_test.dart
@@ -347,4 +347,20 @@ main() {
       expect(range[1], isComment);
     });
   });
+
+  group('iterating', () {
+    test('NodeIterator', () {
+      var root = makeNodeWithChildren();
+      var nodeIterator = new NodeIterator(root, NodeFilter.SHOW_COMMENT);
+      expect(nodeIterator.nextNode(), isComment);
+      expect(nodeIterator.nextNode(), isNull);
+    });
+
+    test('TreeWalker', () {
+      var root = makeNodeWithChildren();
+      var treeWalker = new TreeWalker(root, NodeFilter.SHOW_COMMENT);
+      expect(treeWalker.nextNode(), isComment);
+      expect(treeWalker.nextNode(), isNull);
+    });
+  });
 }