Add a (disabled) test to demonstrate child frame creation race.

chrome/browser/apps/app_browsertest.cc

 // Copyright 2013 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.
 
 #include <stddef.h>
 
 #include <memory>
 
 #include "apps/launcher.h"
 #include "base/bind.h"
@@ skipping 1367 matching lines @@
 
   // Now check that the app window's default zoom, and actual zoom level,
   // have not been changed from the default.
   WebContents* web_contents = GetFirstAppWindowWebContents();
   content::HostZoomMap* app_host_zoom_map = content::HostZoomMap::Get(
       web_contents->GetSiteInstance());
   EXPECT_EQ(0, app_host_zoom_map->GetDefaultZoomLevel());
   EXPECT_EQ(0, app_host_zoom_map->GetZoomLevel(web_contents));
 }
 
+// This test will flake until we fix the underlying issue:
+// https://crbug.com/620194.
+#define MAYBE_AppWindowIframe DISABLED_AppWindowIframe
+// Sends chrome.test.sendMessage from chrome.app.window.create's callback.
+// The app window also adds an <iframe> to the page during window.onload.
+IN_PROC_BROWSER_TEST_F(PlatformAppBrowserTest, MAYBE_AppWindowIframe) {
+  LoadAndLaunchPlatformApp("app_window_send_message",
+                           "APP_WINDOW_CREATE_CALLBACK");
+}
+
 }  // namespace extensions