Remove third_party/polymer from .gitignore

third_party/polymer/v1_0/components/more-routing/params.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="emitter.html">
-
-<script>
-(function(scope) {
-var MoreRouting = scope.MoreRouting = scope.MoreRouting || {};
-MoreRouting.Params = Params;
-
-/**
- * A collection of route parameters and their values, with nofications.
- *
- * Params prefixed by `__` are reserved.
- *
- * @param {!Array<string>} params The keys of the params being managed.
- * @param {Params=} parent A parent route's params to inherit.
- * @return {Params}
- */
-function Params(params, parent) {
-  var model = Object.create(parent || Params.prototype);
-  // We have a different set of listeners at every level of the hierarchy.
-  Object.defineProperty(model, '__listeners', {value: []});
-
-  // We keep all state enclosed within this closure so that inheritance stays
-  // relatively straightfoward.
-  var state = {};
-  _compile(model, params, state);
-
-  return model;
-}
-Params.prototype = Object.create(MoreRouting.Emitter);
-
-// Utility
-
-function _compile(model, params, state) {
-  params.forEach(function(param) {
-    Object.defineProperty(model, param, {
-      get: function() {
-        return state[param];
-      },
-      set: function(value) {
-        if (state[param] === value) return;
-        state[param] = value;
-        model.__notify(param, value);
-      },
-    });
-  });
-}
-
-})(window);
-</script>