Pull web-animations-js into third-party via the third_party/polymer/reproduce.sh script. Add necess…

third_party/web-animations-js/sources/src/element-animatable.js

+// Copyright 2014 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+//     You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//     See the License for the specific language governing permissions and
+// limitations under the License.
+
+(function(scope) {
+  window.Element.prototype.animate = function(effectInput, timingInput) {
+    return scope.timeline._play(scope.Animation(this, effectInput, timingInput));
+  };
+})(webAnimations1);