[dart:html] rename register to registerElement per spec

tools/dom/templates/html/impl/impl_Document.darttemplate

 // Copyright (c) 2012, 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.
 
 part of $LIBRARYNAME;
 
 @DocsEditable()
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME extends Node $NATIVESPEC
 {
 
@@ skipping 30 matching lines @@
   /**
    * Alias for [querySelectorAll]. Note this function is deprecated because its
    * semantics will be changing in the future.
    */
   @deprecated
   @Experimental()
   @DomName('Document.querySelectorAll')
   ElementList queryAll(String relativeSelectors) =>
       querySelectorAll(relativeSelectors);
 
-  /// Checks if [register] is supported on the current platform.
-  bool get supportsRegister {
+  /// Checks if [registerElement] is supported on the current platform.
+  bool get supportsRegisterElement {
 $if DART2JS
     return JS('bool', '("registerElement" in #)', this);
 $else
     return true;
 $endif
   }
 
+  /// *Deprecated*: use [supportsRegisterElement] instead.
+  @deprecated
+  bool get supportsRegister => supportsRegisterElement;
+
   @DomName('Document.createElement')
   Element createElement(String tagName, [String typeExtension]) {
 $if DART2JS
     return _createElement(tagName, typeExtension);
 $else
     if (typeExtension != null) {
       return _createElement(tagName, typeExtension);
     } else {
       // Fast-path for Dartium when typeExtension is not needed.
       return _Utils.createElement(this, tagName);
     }
 $endif
   }
 
 $if DART2JS
   @DomName('Document.createNodeIterator')
   NodeIterator _createNodeIterator(Node root,
       [int whatToShow, NodeFilter filter])
       => JS('NodeIterator', '#.createNodeIterator(#, #, #, false)',
           this, root, whatToShow, filter);
 
   @DomName('Document.createTreeWalker')
   TreeWalker _createTreeWalker(Node root,
       [int whatToShow, NodeFilter filter])
       => JS('TreeWalker', '#.createTreeWalker(#, #, #, false)',
           this, root, whatToShow, filter);
 $endif
 }