update polymer and platform.js

pkg/polymer/lib/src/js/use_native_dartium_shadowdom.js

-// Prevent polyfilled JS Shadow DOM in Dartium
-// We need this if we want Dart code to be able to interoperate with Polymer.js
-// code that also uses Shadow DOM.
-// TODO(jmesserly): we can remove this code once platform.js is correctly
-// feature detecting Shadow DOM in Dartium.
-if (navigator.userAgent.indexOf('(Dart)') !== -1) {
-  window.Platform = window.Platform || {};
-  Platform.flags = Platform.flags || {};
-  Platform.flags.shadow = 'native';
-
-  // Note: Dartium 34 hasn't turned on the unprefixed Shadow DOM
-  // (this happens in Chrome 35), so unless "enable experimental platform
-  // features" is enabled, things will break. So we expose them as unprefixed
-  // names instead.
-  var proto = Element.prototype;
-  if (!proto.createShadowRoot) {
-    proto.createShadowRoot = proto.webkitCreateShadowRoot;
-
-    Object.defineProperty(proto, 'shadowRoot', {
-      get: function() {
-        return this.webkitShadowRoot;
-      },
-      set: function(value) {
-        this.webkitShadowRoot = value;
-      },
-      configurable: true
-    });
-  }
-}