Make HTMLElement.prototype.constructor configurable and writable

src/CustomElements/v1/CustomElements.js

@@ -639,8 +639,9 @@ var Deferred;
     throw new Error('Unknown constructor. Did you call customElements.define()?');
   }
   win.HTMLElement = newHTMLElement;
-  win.HTMLElement.prototype = Object.create(origHTMLElement.prototype);
-  Object.defineProperty(win.HTMLElement.prototype, 'constructor', {value: win.HTMLElement});
+  win.HTMLElement.prototype = Object.create(origHTMLElement.prototype, {
+    constructor: {value: win.HTMLElement, configurable: true, writable: true},
+  });
 
   // patch all built-in subclasses of HTMLElement to inherit from the new HTMLElement
   // See https://html.spec.whatwg.org/multipage/indices.html#element-interfaces

tests/CustomElements/v1/index.html

@@ -24,6 +24,7 @@
     'js/closure.js',
     'js/upgrade.js',
     'js/shadow-dom.js',
+    'js/patching.js',
     'html/imports.html',
   ]);
 </script>

tests/CustomElements/v1/js/patching.js

@@ -0,0 +1,23 @@
+/**
+ * @license
+ * Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
+ * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+ * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+ * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+ * Code distributed by Google as part of the polymer project is also
+ * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+ */
+
+suite('patching', function() {
+
+  suite('HTMLElement', function () {
+
+    test('constructor is configurable and writable', function() {
+      var descriptor = Object.getOwnPropertyDescriptor(HTMLElement.prototype, 'constructor');
+      assert.isTrue(descriptor.configurable);
+      assert.isTrue(descriptor.writable);
+    });
+
+  });
+
+});