introduce web_components pkg for consolidated polyfills

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();
-  });
+  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);
     }
   }
 }