Added Alan's CL 1398603003 and augmented with upgrade for HtmlElement and HTMLElement

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index 580fcb4d1ba26b2b8eb7bb839183413dbaae48da..e7d064e5f6c942597b207de87812cc0b62b7ba2e 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -51,6 +51,7 @@ import 'dart:web_audio' as web_audio;
 import 'dart:web_audio' show web_audioBlinkMap;
 import 'dart:web_audio' show web_audioBlinkFunctionMap;
 import 'dart:_blink' as _blink;
+import 'dart:developer';
 // 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.
@@ -47090,15 +47091,23 @@ class _VMElementUpgrader implements ElementUpgrader {
   }
 
   Element upgrade(element) {
-    if (element.runtimeType != js.JsObjectImpl) {
-      throw new UnsupportedError('Element is incorrect type');
+    var jsObject;
+    var tag;
+    if (element.runtimeType == HtmlElement) {
+      jsObject = unwrap_jso(element);
+      tag = element.localName;
+    } else if (element.runtimeType == js.JsObjectImpl) {
+      // It's a Polymer core element (written in JS).
+      jsObject = element;
+      tag = element['localName'];
+    } else {
+      throw new UnsupportedError('Element is incorrect type. Got ${element.runtimeType}, expected HtmlElement/JsObjectImpl.');
     }
 
     // Remember Dart class to tagName for any upgrading done in wrap_jso.
-    var tag = element['localName'];
     _knownCustomeElements[tag] = _type;
 
-    return createCustomUpgrader(_nativeType, element);
+    return createCustomUpgrader(_nativeType, jsObject);
   }
 }