MD History: Add lazy-render element for simple lazy initialization.

chrome/test/data/webui/md_history/lazy_render_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.lazy_render_test', function() {
+  function registerTests() {
+    suite('history-lazy-render', function() {
+
+      setup(function() {
+        PolymerTest.clearBody();
+        var template =
+            '<template is="dom-bind" id="bind">' +
+            '  <template is="history-lazy-render" id="lazy">' +
+            '    <h1>' +
+            '      <paper-checkbox checked="{{checked}}"></paper-checkbox>' +
+            '      {{name}}' +
+            '    </h1>' +
+            '  </template>' +
+            '</template>';
+        document.body.innerHTML = template;
+      });
+
+      test('stamps after get()', function() {
+        var lazy = document.getElementById('lazy');
+
+        assertFalse(!!document.body.querySelector('h1'));
+        assertFalse(!!lazy.getIfExists());
+
+        return lazy.get().then(function(inner) {
+          assertEquals('H1', inner.nodeName);
+          assertEquals(inner, document.body.querySelector('h1'));
+        });
+      });
+
+      test('one-way binding works', function() {
+        var bind = document.getElementById('bind');
+        bind.name = 'Wings';
+        var lazy = document.getElementById('lazy');
+
+        return lazy.get().then(function(inner) {
+          assertNotEquals(-1, inner.textContent.indexOf('Wings'));
+          bind.name = 'DC';
+          assertNotEquals(-1, inner.textContent.indexOf('DC'));
+        });
+      });
+
+      test('two-way binding works', function() {
+        var bind = document.getElementById('bind');
+        bind.checked = true;
+
+        var lazy = document.getElementById('lazy');
+
+        return lazy.get().then(function(inner) {
+          var checkbox = document.querySelector('paper-checkbox');
+          assertTrue(checkbox.checked);
+          MockInteractions.tap(checkbox);
+          assertFalse(checkbox.checked);
+          assertFalse(bind.checked);
+        });
+      });
+    });
+  }
+
+  return {
+    registerTests: registerTests,
+  }
+});