[dart:html] rename register to registerElement per spec

tests/html/custom/entered_left_view_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 entered_left_view_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:js' as js;
 import 'package:unittest/html_individual_config.dart';
@@ skipping 59 matching lines @@
 
   var docA = document;
   var docB = document.implementation.createHtmlDocument('');
 
   var nullSanitizer = new NullTreeSanitizer();
 
   var registeredTypes = false;
   setUp(() => customElementsReady.then((_) {
     if (registeredTypes) return;
     registeredTypes = true;
-    document.register('x-a', Foo);
-    document.register('x-a-old', FooOldCallbacks);
+    document.registerElement('x-a', Foo);
+    document.registerElement('x-a-old', FooOldCallbacks);
   }));
 
   group('standard_events', () {
     var a;
     setUp(() {
       invocations = [];
     });
 
     test('Created', () {
       a = new Element.tag('x-a');
@@ skipping 210 matching lines @@
       upgradeCustomElements(div);
       invocations = [];
       document.body.append(div);
       customElementsTakeRecords();
       expect(invocations, ['attached'],
           reason: 'the attached callback should be invoked when inserted into a '
           'document with a view as part of a subtree');
     });
   });
 }