Change NotImplementedException to UnimplementedError.

tests/html/cssstyledeclaration_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 CSSStyleDeclarationTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
   createTestStyle() {
     return new CSSStyleDeclaration.css("""
       color: blue;
       width: 2px !important;
     """);
   };
 
   test('default constructor is empty', () {
     var style = new CSSStyleDeclaration();
     expect(style.cssText, isEmpty);
     expect(style.getPropertyPriority('color'), isEmpty);
     expect(style.item(0), isEmpty);
     expect(style, hasLength(0));
-    // These assertions throw a NotImplementedException in dartium:
+    // These assertions throw a UnimplementedError in dartium:
     // expect(style.parentRule, isNull);
     // expect(style.getPropertyCSSValue('color'), isNull);
     // expect(style.getPropertyShorthand('color'), isNull);
   });
 
   test('length is wrapped', () {
     expect(createTestStyle(), hasLength(2));
   });
 
   test('getPropertyPriority is wrapped', () {
@@ skipping 53 matching lines @@
     window.setTimeout(expectAsync0(() {
       element.style.textDecoration = 'underline';
       element.getComputedStyle('').then(expectAsync1(
         (CSSStyleDeclaration style) {
           expect(style.textDecoration, equals('underline'));
         }
       ));
     }), 10);
   });
 }