introduce web_components pkg for consolidated polyfills

tests/html/custom/document_register_type_extensions_test.dart

 // Copyright (c) 2013, 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 document_register_type_extensions_test;
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_individual_config.dart';
 import 'dart:html';
 import '../utils.dart';
 
@@ skipping 83 matching lines @@
     }
     registeredTypes = true;
     document.register(Foo.tag, Foo);
     document.register(Bar.tag, Bar, extendsTag: 'input');
     document.register(Baz.tag, Baz);
     document.register(Qux.tag, Qux, extendsTag: 'input');
     document.register(MyCanvas.tag, MyCanvas, extendsTag: 'canvas');
     document.register(CustomCustomDiv.tag, CustomCustomDiv, extendsTag: 'div');
   }
 
-  setUp(loadPolyfills);
+  setUp(() => customElementsReady);
 
   group('registration', () {
     setUp(registerTypes);
 
     test('cannot register twice', () {
       expect(() => document.register(FooBad.tag, Foo, extendsTag: 'div'),
           throws);
     });
 
     test('cannot register for non-matching tag', () {
@@ skipping 193 matching lines @@
 
   group('functional', () {
     setUp(registerTypes);
 
     test('canvas', () {
       var canvas = new MyCanvas();
       canvas.fillAsRed();
     });
   });
 }