Remove third_party/polymer from .gitignore

third_party/polymer/v1_0/components/more-routing/more-routing-config.html

-<!--
-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="routing.html">
-<!-- TODO(nevir): import on demand? -->
-<link rel="import" href="driver/hash.html">
-<link rel="import" href="driver/mock.html">
-<link rel="import" href="driver/path.html">
-
-<script>
-
-  Polymer({
-
-    is: 'more-routing-config',
-
-    properties: {
-
-      /**
-       * The routing driver to use.
-       *
-       *  * `hash`: `MoreRouting.HashDriver`
-       *  * `path`: `MoreRouting.PathDriver`
-       *  * `mock`: `MoreRouting.MockDriver`
-       *
-       */
-      driver: String,
-
-      /**
-       *
-       */
-      urlPrefix: String,
-
-    },
-
-    ready: function() {
-      var config = {};
-      if (this.urlPrefix) config.prefix = this.urlPrefix;
-
-      var driver;
-      // TODO(nevir): Support custom drivers, too.
-      if (this.driver === 'hash') {
-        driver = new MoreRouting.HashDriver(config);
-      } else if (this.driver === 'path') {
-        driver = new MoreRouting.PathDriver(config);
-      } else if (this.driver === 'mock') {
-        driver = new MoreRouting.MockDriver(config);
-      } else {
-        throw new Error('Unknown driver type "' + this.driver + '"');
-      }
-
-      MoreRouting.driver = driver;
-    },
-
-  });
-
-</script>