Test wallpaper picker app could launch in dev and stable channel

chrome/browser/resources/chromeos/wallpaper_manager/js/event_page.js

 // Copyright (c) 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.
 
 var WALLPAPER_PICKER_WIDTH = 574;
 var WALLPAPER_PICKER_HEIGHT = 420;
 
 var wallpaperPickerWindow;
 
 var surpriseWallpaper = null;
@@ skipping 214 matching lines @@
     width: WALLPAPER_PICKER_WIDTH,
     height: WALLPAPER_PICKER_HEIGHT,
     resizable: false,
     alphaEnabled: true
   }, function(w) {
     wallpaperPickerWindow = w;
     chrome.wallpaperPrivate.minimizeInactiveWindows();
     w.onClosed.addListener(function() {
       chrome.wallpaperPrivate.restoreMinimizedWindows();
     });
+    WallpaperUtil.testSendMessage('wallpaper-window-created');
   });
 });
 
 chrome.storage.onChanged.addListener(function(changes, namespace) {
   if (changes[Constants.AccessSurpriseMeEnabledKey]) {
     if (changes[Constants.AccessSurpriseMeEnabledKey].newValue) {
       SurpriseWallpaper.getInstance().next();
     } else {
       SurpriseWallpaper.getInstance().disable();
     }
@@ skipping 22 matching lines @@
         WallpaperUtil.saveToStorage(Constants.AccessLocalWallpaperInfoKey,
                                     newValue, false);
       }
     });
   }
 });
 
 chrome.alarms.onAlarm.addListener(function() {
   SurpriseWallpaper.getInstance().next();
 });