Add delete context menu for custom wallpapers and some ui tweaks

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 = 576;
-var WALLPAPER_PICKER_HEIGHT = 422;
+var WALLPAPER_PICKER_WIDTH = 574;
+var WALLPAPER_PICKER_HEIGHT = 420;
 
 /**
  * Key to access wallpaper rss in chrome.local.storage.
  */
 /** @const */ var AccessRssKey = 'wallpaper-picker-surprise-rss-key';
 
 /**
  * Key to access wallpaper manifest in chrome.local.storage.
  */
 /** @const */ var AccessManifestKey = 'wallpaper-picker-manifest-key';
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       chrome.wallpaperPrivate.restoreMinimizedWindows();
     });
   });
 });
 
 chrome.alarms.onAlarm.addListener(function() {
   var nextUpdate = SurpriseWallpaper.getInstance().nextUpdateTime(new Date());
   chrome.alarms.create({when: nextUpdate});
   SurpriseWallpaper.getInstance().tryChangeWallpaper();
 });