fixes to polymer, gets tests back to a stable state

pkg/custom_element/lib/polyfill.dart

Index: pkg/custom_element/lib/polyfill.dart
diff --git a/pkg/custom_element/lib/polyfill.dart b/pkg/custom_element/lib/polyfill.dart
new file mode 100644
index 0000000000000000000000000000000000000000..0d041aad06eeec1e057811c9239eaeedaef066f5
--- /dev/null
+++ b/pkg/custom_element/lib/polyfill.dart
@@ -0,0 +1,42 @@
+// Copyright (c) 2013, 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.
+
+/** Dart APIs for interacting with the JavaScript Custom Elements polyfill. */
+library custom_element.polyfill;
+
+import 'dart:async';
+import 'dart:html';
+import 'dart:js' as js;
+
+/**
+ * A future that completes once all custom elements in the initial HTML page
+ * have been upgraded.
+ *
+ * This is needed because the native implementation can update the elements
+ * while parsing the HTML document, but the custom element polyfill cannot,
+ * so it completes this future once all elements are upgraded.
+ */
+Future customElementsReady = () {
+  if (_isReady) return new Future.value();
+
+  // Not upgraded. Wait for the polyfill to fire the WebComponentsReady event.
+  return document.body.on['WebComponentsReady'].first;
+}();
+
+// Return true if we are using the polyfill and upgrade is complete, or if we
+// have native document.register and therefore the browser took care of it.
+// Otherwise return false, including the case where we can't find the polyfill.
+bool get _isReady {
+  // If we don't have dart:js, assume things are ready
+  if (js.context == null) return true;
+
+  var customElements = js.context['CustomElements'];
+  if (customElements == null) {
+    // Return true if native document.register, otherwise false.
+    // (Maybe the polyfill isn't loaded yet. Wait for it.)
+    return document.supportsRegister;
+  }
+
+  return customElements['ready'] == true;
+}