Remove third_party/polymer from .gitignore

third_party/polymer/v1_0/components/paper-styles/classes/shadow.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
--->
-
-<style>
-.shadow-transition {
-  transition: box-shadow 0.28s cubic-bezier(0.4, 0, 0.2, 1);
-}
-
-.shadow-elevation-2dp {
-  box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.14),
-              0 1px 5px 0 rgba(0, 0, 0, 0.12),
-              0 3px 1px -2px rgba(0, 0, 0, 0.2);
-}
-
-.shadow-elevation-3dp {
-  box-shadow: 0 3px 4px 0 rgba(0, 0, 0, 0.14),
-              0 1px 8px 0 rgba(0, 0, 0, 0.12),
-              0 3px 3px -2px rgba(0, 0, 0, 0.4);
-}
-
-.shadow-elevation-4dp {
-  box-shadow: 0 4px 5px 0 rgba(0, 0, 0, 0.14),
-              0 1px 10px 0 rgba(0, 0, 0, 0.12),
-              0 2px 4px -1px rgba(0, 0, 0, 0.4);
-}
-
-.shadow-elevation-6dp {
-  box-shadow: 0 6px 10px 0 rgba(0, 0, 0, 0.14),
-              0 1px 18px 0 rgba(0, 0, 0, 0.12),
-              0 3px 5px -1px rgba(0, 0, 0, 0.4);
-}
-
-.shadow-elevation-8dp {
-  box-shadow: 0 8px 10px 1px rgba(0, 0, 0, 0.14),
-              0 3px 14px 2px rgba(0, 0, 0, 0.12),
-              0 5px 5px -3px rgba(0, 0, 0, 0.4);
-}
-
-.shadow-elevation-16dp {
-  box-shadow: 0 16px 24px 2px rgba(0, 0, 0, 0.14),
-              0  6px 30px 5px rgba(0, 0, 0, 0.12),
-              0  8px 10px -5px rgba(0, 0, 0, 0.4);
-}
-
-</style>