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 b54fc767e4b5f34949acd24f8a9b146901d4def6..b9db444af8613cdfcc0f4ff17f14566fc0663aef 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -20088,6 +20088,10 @@ class HtmlDocument extends Document {
    */
   void registerElement(String tag, Type customElementClass,
       {String extendsTag}) {
+    // Hack to setup an interceptor for HTMLElement so it isn't changed when a custom element is created.
+    var jsHTMLElementPrototype = js.JsNative.getProperty(js.JsNative.getProperty(js.context, 'HTMLElement'),'prototype');
+    _blink.Blink_Utils.defineInterceptor(jsHTMLElementPrototype, HtmlElement.instanceRuntimeType);
+
     // Figure out which DOM class is being extended from the user's Dart class.
     var classMirror = reflectClass(customElementClass);