Settings WebUI: Update test to not depend on screen size

Change-Id: Ifafd8ad395939011ce9d48e39d04a8d3fcda90cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1610849Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659274}

chrome/test/data/webui/settings/settings_ui_browsertest.js

@@ -48,8 +48,12 @@ TEST_F('SettingsUIBrowserTest', 'MAYBE_All', function() {
       Polymer.dom.flush();
     });
 
-    test('showing menu in toolbar', function() {
+    test('showing menu in toolbar is dependent on narrow mode', function() {
       toolbar = assert(ui.$$('cr-toolbar'));
+      toolbar.narrow = true;
+      assertTrue(toolbar.showMenu);
+
+      toolbar.narrow = false;
       assertFalse(toolbar.showMenu);
     });