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

tools/dom/templates/html/impl/impl_HTMLDocument.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.
 
 // WARNING: Do not edit - generated code.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
 $!MEMBERS
@@ skipping 352 matching lines @@
       throw new DomException.jsInterop("HierarchyRequestError: Only HTML elements can be customized.");
     }
 
     if (_hasCreatedConstructor(classMirror)) {
       // Start the hookup the JS way create an <x-foo> element that extends the
       // <x-base> custom element. Inherit its prototype and signal what tag is
       // inherited:
       //
       //     var myProto = Object.create(HTMLElement.prototype);
       //     var myElement = document.registerElement('x-foo', {prototype: myProto});
-      var baseElement = js.context[jsClassName];
+      var baseElement = js.JsNative.getProperty(js.context, jsClassName);
       if (baseElement == null) {
         // Couldn't find the HTML element so use a generic one.
-        baseElement = js.context['HTMLElement'];
+        baseElement = js.JsNative.getProperty(js.context, 'HTMLElement');
       }
-      var elemProto = js.context['Object'].callMethod("create", [baseElement['prototype']]);
+      var elemProto = js.JsNative.callMethod(js.JsNative.getProperty(js.context, 'Object'), "create", [js.JsNative.getProperty(baseElement, 'prototype')]);
 
       // Remember for any upgrading done in wrap_jso.
       _knownCustomeElements[tag] = customElementClass;
 
       // TODO(terry): Hack to stop recursion re-creating custom element when the
       //              created() constructor of the custom element does e.g.,
       //
       //                  MyElement.created() : super.created() {
       //                    this.innerHtml = "<b>I'm an x-foo-with-markup!</b>";
       //                  }
       //
       //              sanitizing causes custom element to created recursively
       //              until stack overflow.
       //
       //              See https://github.com/dart-lang/sdk/issues/23666
       int creating = 0;
-      elemProto['createdCallback'] = new js.JsFunction.withThis(($this) {
+      // TODO(jacobr): warning: 
+      elemProto['createdCallback'] = js.JsNative.withThis(($this) {
         if (_getJSClassName(reflectClass(customElementClass).superclass) != null && creating < 2) {
           creating++;
 
           var dartClass;
           try {
             dartClass = _blink.Blink_Utils.constructElement(customElementClass, $this);
           } catch (e) {
             dartClass = HtmlElement.internalCreateHtmlElement();
             throw e;
           } finally {
             // Need to remember the Dart class that was created for this custom so
             // return it and setup the blink_jsObject to the $this that we'll be working
             // with as we talk to blink. 
-            $this['dart_class'] = dartClass;
+            js.setDartHtmlWrapperFor($this, dartClass);
 
             creating--;
           }
         }
       });
       elemProto['attributeChangedCallback'] = new js.JsFunction.withThis(($this, attrName, oldVal, newVal) {
-        if ($this["dart_class"] != null && $this['dart_class'].attributeChanged != null) {
-          $this['dart_class'].attributeChanged(attrName, oldVal, newVal);
-        }
+        $this.attributeChanged(attrName, oldVal, newVal);
       });
       elemProto['attachedCallback'] = new js.JsFunction.withThis(($this) {
-        if ($this["dart_class"] != null && $this['dart_class'].attached != null) {
-          $this['dart_class'].attached();
-        }
+        $this.attached();
       });
       elemProto['detachedCallback'] = new js.JsFunction.withThis(($this) {
-        if ($this["dart_class"] != null && $this['dart_class'].detached != null) {
-          $this['dart_class'].detached();
-        }
+        $this.detached();
       });
       // document.registerElement('x-foo', {prototype: elemProto, extends: extendsTag});
       var jsMap = new js.JsObject.jsify({'prototype': elemProto, 'extends': extendsTag});
-      js.context['document'].callMethod('registerElement', [tag, jsMap]);
+      js.Jsnative.callMethod(js.JsNative.getProperty(js.context, 'document'), 'registerElement', [tag, jsMap]);
     }
 $endif
   }
 
   /** *Deprecated*: use [registerElement] instead. */
   @deprecated
   @Experimental()
   void register(String tag, Type customElementClass, {String extendsTag}) {
     return registerElement(tag, customElementClass, extendsTag: extendsTag);
   }
@@ skipping 48 matching lines @@
   /// parameter must be provided.
   @Experimental()
   ElementUpgrader createElementUpgrader(Type type, {String extendsTag}) {
 $if DART2JS
     return new _JSElementUpgrader(this, type, extendsTag);
 $else
     return new _VMElementUpgrader(this, type, extendsTag);
 $endif
   }
 }