Settings Router Refactor: Update subpage-back button to use history back sometimes.

chrome/test/data/webui/settings/settings_subpage_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('settings_subpage', function() {
+  function registerTests() {
+    suite('SettingsSubpage', function() {
+      test('can navigate to parent', function() {
+        PolymerTest.clearBody();
+
+        // Choose CERTIFICATES since it is not a descendant of BASIC.
+        settings.navigateTo(settings.Route.CERTIFICATES);
+        assertEquals(settings.Route.CERTIFICATES, settings.getCurrentRoute());
+
+        var subpage = document.createElement('settings-subpage');
+        document.body.appendChild(subpage);
+
+        MockInteractions.tap(subpage.$$('paper-icon-button'));
+        assertEquals(settings.Route.PRIVACY, settings.getCurrentRoute());
+      });
+
+      test('can navigate to grandparent using window.back()', function(done) {
+        PolymerTest.clearBody();
+
+        settings.navigateTo(settings.Route.BASIC);
+        settings.navigateTo(settings.Route.SYNC);
+        assertEquals(settings.Route.SYNC, settings.getCurrentRoute());
+
+        var subpage = document.createElement('settings-subpage');
+        document.body.appendChild(subpage);
+
+        MockInteractions.tap(subpage.$$('paper-icon-button'));
+
+        // Since the previous history entry is an ancestor, we expect
+        // window.history.back() to be called and a popstate event to be fired.
+        window.addEventListener('popstate', function(event) {
+          assertEquals(settings.Route.BASIC, settings.getCurrentRoute());
+          done();
+        });
+      });
+    });
+  }
+
+  return {
+    registerTests: registerTests,
+  };
+});