Flip --enable-apps-show-on-first-paint flag.

chrome/common/extensions/api/app_window.idl

 // Copyright (c) 2012 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.
 
 // Use the <code>chrome.app.window</code> API to create windows. Windows
 // have an optional frame with title bar and size controls. They are not
 // associated with any Chrome browser windows.
 namespace app.window {
 
   // Previously named Bounds.
@@ skipping 411 matching lines @@
     [nocompile] static void onFullscreened();
 
     // Fired when the window is maximized.
     [nocompile] static void onMaximized();
 
     // Fired when the window is minimized.
     [nocompile] static void onMinimized();
 
     // Fired when the window is restored from being minimized or maximized.
     [nocompile] static void onRestored();
+
+    // Event for testing. Lets tests wait until a window has been shown.
+    [nocompile, nodoc] static void onWindowFirstShown();
   };
 };