MD History: Hook all elements into the page and add tests.

chrome/test/data/webui/md_history/test_util.js

Index: chrome/test/data/webui/md_history/test_util.js
diff --git a/chrome/test/data/webui/md_history/test_util.js b/chrome/test/data/webui/md_history/test_util.js
new file mode 100644
index 0000000000000000000000000000000000000000..acb77f4d03142d9242589f033837ae2174594dd1
--- /dev/null
+++ b/chrome/test/data/webui/md_history/test_util.js
@@ -0,0 +1,12 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/*
+ * Waits for queued up tasks to finish before proceeding. Inspired by:
+ * https://github.com/Polymer/web-component-tester/blob/master/browser/environment/helpers.js#L97
+ */
+function flush(callback) {
+  Polymer.dom.flush();
+  window.setTimeout(callback, 0);
+}