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;
 
 var wallpaperPickerWindow;
 
 chrome.app.runtime.onLaunched.addListener(function() {
   if (wallpaperPickerWindow && !wallpaperPickerWindow.contentWindow.closed) {
     wallpaperPickerWindow.focus();
     chrome.wallpaperPrivate.minimizeInactiveWindows();
     return;
   }
 
   chrome.app.window.create('main.html', {
     frame: 'none',
     width: WALLPAPER_PICKER_WIDTH,
     height: WALLPAPER_PICKER_HEIGHT,
     minWidth: WALLPAPER_PICKER_WIDTH,
     maxWidth: WALLPAPER_PICKER_WIDTH,
     minHeight: WALLPAPER_PICKER_HEIGHT,
     maxHeight: WALLPAPER_PICKER_HEIGHT,
     transparentBackground: true
   }, function(w) {
     wallpaperPickerWindow = w;
     chrome.wallpaperPrivate.minimizeInactiveWindows();
     w.onClosed.addListener(function() {
       chrome.wallpaperPrivate.restoreMinimizedWindows();
     });
   });
 });