[polymer] interop with polymer-element and polymer.js

pkg/polymer/lib/src/boot.dart

-// 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.
-
-/// Ported from `polymer/src/boot.js`. *
-part of polymer;
-
-/// Prevent a flash of unstyled content.
-_preventFlashOfUnstyledContent() {
-
-  var style = new StyleElement();
-  style.text = '.$_VEILED_CLASS { '
-      'opacity: 0; } \n'
-      '.$_UNVEIL_CLASS{ '
-      '-webkit-transition: opacity ${_TRANSITION_TIME}s; '
-      'transition: opacity ${_TRANSITION_TIME}s; }\n';
-
-  // Note: we use `query` and not `document.head` to make sure this code works
-  // with the shadow_dom polyfill (a limitation of the polyfill is that it can't
-  // override the definitions of document, document.head, or document.body).
-  var head = document.querySelector('head');
-  head.insertBefore(style, head.firstChild);
-
-  _veilElements();
-
-  // hookup auto-unveiling
-  Polymer.onReady.then((_) => Polymer.unveilElements());
-}
-
-// add polymer styles
-const _VEILED_CLASS = 'polymer-veiled';
-const _UNVEIL_CLASS = 'polymer-unveil';
-const _TRANSITION_TIME = 0.3;
-
-// apply veiled class
-_veilElements() {
-  for (var selector in Polymer.veiledElements) {
-    for (var node in document.querySelectorAll(selector)) {
-      node.classes.add(_VEILED_CLASS);
-    }
-  }
-}