Remove third_party/polymer from .gitignore

third_party/polymer/v1_0/components/neon-animation/neon-shared-element-animation-behavior.html

-<!--
-@license
-Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
-This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
-The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
-The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
-Code distributed by Google as part of the polymer project is also
-subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
--->
-
-<link rel="import" href="../polymer/polymer.html">
-<link rel="import" href="neon-animation-behavior.html">
-
-<script>
-
-  /**
-   * Use `Polymer.NeonSharedElementAnimationBehavior` to implement shared element animations.
-   * @polymerBehavior Polymer.NeonSharedElementAnimationBehavior
-   */
-  Polymer.NeonSharedElementAnimationBehaviorImpl = {
-
-    properties: {
-
-      /**
-       * Cached copy of shared elements.
-       */
-      sharedElements: {
-        type: Object
-      }
-
-    },
-
-    /**
-     * Finds shared elements based on `config`.
-     */
-    findSharedElements: function(config) {
-      var fromPage = config.fromPage;
-      var toPage = config.toPage;
-      if (!fromPage || !toPage) {
-        console.warn(this.is + ':', !fromPage ? 'fromPage' : 'toPage', 'is undefined!');
-        return null;
-      };
-
-      if (!fromPage.sharedElements || !toPage.sharedElements) {
-        console.warn(this.is + ':', 'sharedElements are undefined for', !fromPage.sharedElements ? fromPage : toPage);
-        return null;
-      };
-
-      var from = fromPage.sharedElements[config.id]
-      var to = toPage.sharedElements[config.id];
-
-      if (!from || !to) {
-        console.warn(this.is + ':', 'sharedElement with id', config.id, 'not found in', !from ? fromPage : toPage);
-        return null;
-      }
-
-      this.sharedElements = {
-        from: from,
-        to: to
-      };
-      return this.sharedElements;
-    }
-
-  };
-
-  /** @polymerBehavior Polymer.NeonSharedElementAnimationBehavior */
-  Polymer.NeonSharedElementAnimationBehavior = [
-    Polymer.NeonAnimationBehavior,
-    Polymer.NeonSharedElementAnimationBehaviorImpl
-  ];
-
-</script>