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

chrome/renderer/resources/extensions/app_window_custom_bindings.js

 // 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.
 
 // Custom binding for the app_window API.
 
 var appWindowNatives = requireNative('app_window_natives');
 var runtimeNatives = requireNative('runtime');
 var Binding = require('binding').Binding;
 var Event = require('event_bindings').Event;
@@ skipping 195 matching lines @@
     forEach(currentWindowInternal, function(key, value) {
       // Do not add internal functions that should not appear in the AppWindow
       // interface. They are called by Bounds mutators.
       if (key !== kSetBoundsFunction && key !== kSetSizeConstraintsFunction)
         AppWindow.prototype[key] = value;
     });
     AppWindow.prototype.moveTo = $Function.bind(window.moveTo, window);
     AppWindow.prototype.resizeTo = $Function.bind(window.resizeTo, window);
     AppWindow.prototype.contentWindow = window;
     AppWindow.prototype.onClosed = new Event();
+    AppWindow.prototype.onWindowFirstShown = new Event();
     AppWindow.prototype.close = function() {
       this.contentWindow.close();
     };
     AppWindow.prototype.getBounds = function() {
       // This is to maintain backcompatibility with a bug on Windows and
       // ChromeOS, which returns the position of the window but the size of
       // the content.
       var innerBounds = appWindowData.innerBounds;
       var outerBounds = appWindowData.outerBounds;
       return { left: outerBounds.left, top: outerBounds.top,
@@ skipping 107 matching lines @@
     dispatchEventIfExists(currentWindow, "onMinimized");
   if (!oldData.maximized && update.maximized)
     dispatchEventIfExists(currentWindow, "onMaximized");
 
   if ((oldData.fullscreen && !update.fullscreen) ||
       (oldData.minimized && !update.minimized) ||
       (oldData.maximized && !update.maximized))
     dispatchEventIfExists(currentWindow, "onRestored");
 };
 
+function onAppWindowFirstShown() {
+  if (!currentAppWindow)
+    return;
+
+  dispatchEventIfExists(currentAppWindow, "onWindowFirstShown");
+}
+
 function onAppWindowClosed() {
   if (!currentAppWindow)
     return;
   dispatchEventIfExists(currentAppWindow, "onClosed");
 }
 
 function updateBounds(boundsType, bounds) {
   if (!currentWindowInternal)
     return;
 
@@ skipping 11 matching lines @@
     if (value === null)
       constraints[key] = 0;
   });
 
   currentWindowInternal.setSizeConstraints(boundsType, constraints);
 }
 
 exports.binding = appWindow.generate();
 exports.onAppWindowClosed = onAppWindowClosed;
 exports.updateAppWindowProperties = updateAppWindowProperties;
+exports.appWindowFirstShown = onAppWindowFirstShown;