[dart:html] rename register to registerElement per spec

tests/html/custom/template_wrappers_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 template_wrappers_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:js' as js;
 import 'package:unittest/html_config.dart';
@@ skipping 12 matching lines @@
 }
 
 main() {
   useHtmlConfiguration();
 
   setUp(() => customElementsReady);
 
   test('element is upgraded once', () {
 
     expect(createdCount, 0);
-    document.register('x-custom', CustomElement);
+    document.registerElement('x-custom', CustomElement);
     expect(createdCount, 0);
 
     var element = document.createElement('x-custom');
     expect(createdCount, 1);
 
     forceGC();
 
     return new Future.delayed(new Duration(milliseconds: 50)).then((_) {
       var t = document.querySelector('.t1');
 
       var fragment = t.content;
 
       fragment.querySelector('x-custom').attributes['foo'] = 'true';
       expect(createdCount, 1);
     });
   });
 /*
   test('old wrappers do not cause multiple upgrades', () {
     createdCount = 0;
     var d1 = document.querySelector('x-custom-two');
     d1.attributes['foo'] = 'bar';
     d1 = null;
 
-    document.register('x-custom-two', CustomElement);
+    document.registerElement('x-custom-two', CustomElement);
 
     expect(createdCount, 1);
 
     forceGC();
 
     return new Future.delayed(new Duration(milliseconds: 50)).then((_) {
       var d = document.querySelector('x-custom-two');
       expect(createdCount, 1);
     });
   });
 */
 }
 
 
 void forceGC() {
   var N = 1000000;
   var M = 100;
   for (var i = 0; i < M; ++i) {
     var l = new List(N);
   }
 }