Disable Delete option for custom wallpapers when 'Surprise Me' is enabled.

chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.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.
 
 /**
  * WallpaperManager constructor.
  *
  * WallpaperManager objects encapsulate the functionality of the wallpaper
  * manager extension.
  *
@@ skipping 185 matching lines @@
    * @private
    */
   WallpaperManager.prototype.toggleSurpriseMe_ = function() {
     var self = this;
     var checkbox = $('surprise-me').querySelector('#checkbox');
     var shouldEnable = !checkbox.classList.contains('checked');
     var onSuccess = function() {
       if (chrome.runtime.lastError == null) {
         if (shouldEnable) {
           checkbox.classList.add('checked');
+          if (self.document_.body.hasAttribute('custom'))
+            self.document_.body.removeAttribute('custom');

[bshe, 2015/07/15 18:40:49]

custom should only be used to indicate if we are at custom wallpaper tab.
Changing this property based on the state of surprise me feature is kind of
unexpected. We probably want to introduce a new property and use css rules to
hide the context menu. WDYT?

           // Hides the wallpaper set by message if there is any.
           $('wallpaper-set-by-message').textContent = '';
         } else {
           // Unchecking the "Surprise me" checkbox falls back to the previous
           // wallpaper before "Surprise me" was turned on.
           if (self.wallpaperGrid_.activeItem) {
             self.setSelectedWallpaper_(self.wallpaperGrid_.activeItem);
             self.onWallpaperChanged_(self.wallpaperGrid_.activeItem,
                                      self.currentWallpaper_);
           }
+          var selectedIndex = self.categoriesList_.selectionModel.selectedIndex;
+          if (selectedIndex == self.categoriesList_.dataModel.length - 1)
+            self.document_.body.setAttribute('custom', '');
           checkbox.classList.remove('checked');
         }
         $('categories-list').disabled = shouldEnable;
         $('wallpaper-grid').disabled = shouldEnable;
       } else {
         // TODO(bshe): show error message to user.
         console.error('Failed to save surprise me option to chrome storage.');
       }
     };
 
@@ skipping 880 matching lines @@
       }
       this.wallpaperGrid_.dataModel = wallpapersDataModel;
       if (selectedItem) {
         this.wallpaperGrid_.selectedItem = selectedItem;
         this.wallpaperGrid_.activeItem = selectedItem;
       }
     }
   };
 
 })();