Remove third_party/polymer from .gitignore

third_party/polymer/v1_0/components/more-routing/driver/path.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="../driver.html">
-
-<script>
-(function(scope) {
-var MoreRouting = scope.MoreRouting = scope.MoreRouting || {};
-MoreRouting.PathDriver = PathDriver;
-
-/**
- * TODO(nevir): Docs.
- */
-function PathDriver() {
-  MoreRouting.Driver.apply(this, arguments);
-  this._bindEvents();
-  this._read();
-}
-PathDriver.prototype = Object.create(MoreRouting.Driver.prototype);
-
-PathDriver.prototype.navigateToUrl = function navigateToUrl(url) {
-  window.history.pushState({}, '', url);
-  this._read();
-};
-
-PathDriver.prototype._bindEvents = function _bindEvents() {
-  window.addEventListener('popstate', this._read.bind(this));
-};
-
-PathDriver.prototype._read = function _read() {
-  this.setCurrentPath(window.location.pathname);
-};
-
-})(window);
-</script>