Dartium typed js interop work dart repo side of the change. Also tries to get

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()
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME extends Node
 {
 
@@ skipping 56 matching lines @@
     if (typeExtension == null) {
       return _createElement_2(tagName);
     } else {
       return _createElement(tagName, typeExtension);
     }
 $else
     var newElement = (typeExtension == null) ?
       _blink.BlinkDocument.instance.createElement_Callback_1_(unwrap_jso(this), tagName) :
       _blink.BlinkDocument.instance.createElement_Callback_2_(unwrap_jso(this), tagName, typeExtension);
 
-    var wrapped;
-
-    if (newElement['dart_class'] != null) {
-      wrapped = newElement['dart_class'];         // Here's our Dart class.
+    var wrapped = js.getDartHtmlWrapperFor(newElement);  // Here's our Dart class.
+    if (wrapped != null) {
       wrapped.blink_jsObject = newElement;
     } else {
       wrapped = wrap_jso(newElement);
       if (wrapped == null) {
         wrapped = wrap_jso_custom_element(newElement);
       } else {
-        wrapped.blink_jsObject['dart_class'] = wrapped;
+        js.setDartHtmlWrapperFor(wrapped.blink_jsObject, wrapped);
       }
     }
 
     return wrapped;
 $endif
   }
 
 $if DART2JS
   // The two-argument version of this is automatically generated, but we need to
   // omit the typeExtension if it's null on Firefox or we get an is="null" attribute.
@@ skipping 16 matching lines @@
     } else {
       return _createElementNS(namespaceURI, qualifiedName, typeExtension);
     }
 $else
     var newElement = (typeExtension == null) ?
       _blink.BlinkDocument.instance.createElementNS_Callback_2_(unwrap_jso(this), namespaceURI, qualifiedName) :
       _blink.BlinkDocument.instance.createElementNS_Callback_3_(unwrap_jso(this), namespaceURI, qualifiedName, typeExtension);
 
     var wrapped;
 
-    if (newElement['dart_class'] != null) {
-      wrapped = newElement['dart_class'];         // Here's our Dart class.
+    wrapped = js.getDartHtmlWrapperFor(newElement);  // Here's our Dart class.
+    if (wrapped != null) {
       wrapped.blink_jsObject = newElement;
     } else {
       wrapped = wrap_jso(newElement);
       if (wrapped == null) {
         wrapped = wrap_jso_custom_element(newElement);
       } else {
-        wrapped.blink_jsObject['dart_class'] = wrapped;
+        js.setDartHtmlWrapperFor(wrapped.blink_jsObject, wrapped);  // Here's our Dart class.
       }
     }
 
     return wrapped;
 $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
 }