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

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

Index: chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
diff --git a/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js b/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
index b82d5cdce3ca21fa79a2eec14bd6761904ced6db..a0c6b3df8d77c48c6b717d0b722daaf73cb25bec 100644
--- a/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
+++ b/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
@@ -203,6 +203,8 @@ function WallpaperManager(dialogDom) {
       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 {
@@ -213,6 +215,9 @@ function WallpaperManager(dialogDom) {
             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;