Disable surprise me automatically if the current wallpaper was set by a third party application.

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 57af6ad1302f728708f9a918fdd3c5856cc391e3..5d638ecbc448f4446ec4fd6cd1d751026ef33548 100644
--- a/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
+++ b/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
@@ -203,12 +203,16 @@ function WallpaperManager(dialogDom) {
       if (chrome.runtime.lastError == null) {
           if (shouldEnable) {
             checkbox.classList.add('checked');
+            // Hides the wallpaper set by message if there is any.
+            $('wallpaper-set-by-message').textContent = '';

[bshe, 2015/03/13 21:02:44]

I think we should display wallpaper set by message if the current wallpaper is
not set by our wallpaper picker.

Perhaps a 3rd party wallpaper change should disable surprise me feature
automatically. User dont expect their wallpaper changed to a new one the second
day they changed their wallpaper through 3rd party app.

           } else {
             // Unchecking the "Surprise me" checkbox falls back to the previous
             // wallpaper before "Surprise me" was turned on.
-            self.setSelectedWallpaper_(self.wallpaperGrid_.activeItem_);
-            self.onWallpaperChanged_(self.wallpaperGrid_.activeItem_,
-                                     self.currentWallpaper_);
+            if (self.wallpaperGrid_.activeItem) {
+              self.setSelectedWallpaper_(self.wallpaperGrid_.activeItem);
+              self.onWallpaperChanged_(self.wallpaperGrid_.activeItem,
+                                       self.currentWallpaper_);
+            }
             checkbox.classList.remove('checked');
           }
           $('categories-list').disabled = shouldEnable;