Prepare Polymer 2 tests

Include an empty file - this will be filled with Polymer 2 specific code
later, and it's useful to have the empty file now because the Polymer 2
change will likely be pending very long, and we would like to avoid
conflicts keeping so many files in a pending change for long.

Also include a harmless polyfill that we need for Polymer 2.

Change-Id: I504e52ae937edff1d35b29700882b522ef4dbc64
diff --git a/polygerrit-ui/app/elements/shared/gr-storage/gr-storage_test.html b/polygerrit-ui/app/elements/shared/gr-storage/gr-storage_test.html
index 7f2802f..0482584 100644
--- a/polygerrit-ui/app/elements/shared/gr-storage/gr-storage_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-storage/gr-storage_test.html
@@ -17,6 +17,8 @@
 -->
 <meta name="viewport" content="width=device-width, minimum-scale=1.0, initial-scale=1.0, user-scalable=yes">
 <title>gr-storage</title>
+<script src="/test/common-test-setup.js"></script>
+<script src="/bower_components/webcomponentsjs/custom-elements-es5-adapter.js"></script>
 
 <script src="/bower_components/webcomponentsjs/webcomponents-lite.js"></script>
 <script src="/bower_components/web-component-tester/browser.js"></script>