Fixing Node.nodes.first.

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 88 matching lines @@
   });
 
   group('nodes', () {
     test('is a NodeList', () {
       expect(makeNodeWithChildren().nodes, isNodeList);
     });
 
     test('first', () {
       var node = makeNodeWithChildren();
       expect(node.nodes.first, isText);
+
+      node = new DivElement();
+      expect(() {
+        node = node.nodes.first;
+      }, throwsStateError);
     });
 
     test('last', () {
       var node = makeNodeWithChildren();
       expect(node.nodes.last, isComment);
     });
 
     test('forEach', () {
       var nodes = [];
       var node = makeNodeWithChildren();
@@ skipping 140 matching lines @@
     });
 
     test('getRange', () {
       var range = makeNodeList().getRange(1, 2);
       expect(range, isNodeList);
       expect(range[0], isBRElement);
       expect(range[1], isComment);
     });
   });
 }