Change NotImplementedException to UnimplementedError.

tests/html/documentfragment_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 DocumentFragmentTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 part 'util.dart';
 
@@ skipping 25 matching lines @@
       }
     }
     expect(true, isFalse, reason: 'Expected immutability error');
   };
 
   void expectEmptyStyleDeclaration(CSSStyleDeclaration style) {
     expect(style.cssText, equals(''));
     expect(style.getPropertyPriority('color'), equals(''));
     expect(style.item(0), equals(''));
     expect(style.length, isZero);
-    // TODO(jacobr): these checks throw NotImplementedExceptions in dartium.
+    // TODO(jacobr): these checks throw UnimplementedErrors in dartium.
     // expect(style.parentRule, isNull);
     // expect(style.getPropertyCSSValue('color'), isNull);
     // expect(style.getPropertyShorthand('color'), isNull);
     // expect(style.isPropertyImplicit('color'), isFalse);
 
     // Ideally these would throw errors, but it's not possible to create a class
     // that'll intercept these calls without implementing the entire
     // CSSStyleDeclaration interface, so we'll settle for them being no-ops.
     style.cssText = '* {color: blue}';
     style.removeProperty('color');
@@ skipping 294 matching lines @@
   //   // assertConstError(() => fragment.classes.add('foo'));
   // });
 
   test('query searches the fragment', () {
     var fragment = new DocumentFragment.html(
       "<div class='foo'><a>foo</a><b>bar</b></div>");
     expect(fragment.query(".foo a").tagName, "A");
     expect(_nodeStrings(fragment.queryAll(".foo *")), equals(["A", "B"]));
   });
 }