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

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

+// 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.
+
+cr.define('md_history.history_card_test', function() {
+  function registerTests() {
+    suite('history-card', function() {
+      test('basic separator insertion', function() {
+        var element = document.createElement('history-card');
+        element.historyItems = [
+          {"time": "1000000000"},
+          {"time": "10000000"},
+          {"time": "900000"}
+        ];
+        flush(function() {
+          // Check that the correct number of time gaps are inserted.
+          var spacers =
+              Polymer.dom(element.root).querySelectorAll('#time-gap-separator');
+          assertEquals(2, spacers.length);
+        });
+      });
+    });
+  }
+  return {
+    registerTests: registerTests
+  };
+});