Remove third_party/polymer from .gitignore

third_party/polymer/v1_0/components/paper-item/paper-item-shared.css

-/*
-    @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
-*/
-
-:host {
-  display: block;
-  min-height: var(--paper-item-min-height, 48px);
-  padding: 0px 16px;
-}
-
-:host > ::content > *:not(:first-child):not(:last-child) {
-  margin-right: 16px;
-}