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

chrome/browser/apps/app_browsertest.cc

Index: chrome/browser/apps/app_browsertest.cc
diff --git a/chrome/browser/apps/app_browsertest.cc b/chrome/browser/apps/app_browsertest.cc
index 8a96c4442b170d8c5ec263318f9d98ab5ef108a7..fcc1f00052e704b44ddca8f6a7b2f065ec456bac 100644
--- a/chrome/browser/apps/app_browsertest.cc
+++ b/chrome/browser/apps/app_browsertest.cc
@@ -1385,4 +1385,14 @@ IN_PROC_BROWSER_TEST_F(PlatformAppBrowserTest, AppsIgnoreDefaultZoom) {
   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