Remove "set wallpaper..." option in system context menu when guest logged in

chrome/browser/chromeos/background/desktop_background_observer.cc

Index: chrome/browser/chromeos/background/desktop_background_observer.cc
diff --git a/chrome/browser/chromeos/background/desktop_background_observer.cc b/chrome/browser/chromeos/background/desktop_background_observer.cc
index 49f7eff5190c9d32dd5473b8babd2e5e26b1ef51..63de529127118fdeeeb3c40b7e8aff388453b217 100644
--- a/chrome/browser/chromeos/background/desktop_background_observer.cc
+++ b/chrome/browser/chromeos/background/desktop_background_observer.cc
@@ -37,6 +37,10 @@ class UserWallpaperDelegate: public ash::UserWallpaperDelegate {
     browser->ShowOptionsTab("setWallpaper");
   }
 
+  virtual bool IsLoggedInAsGuest() OVERRIDE {
+    return chromeos::UserManager::Get()->IsLoggedInAsGuest();
+  }
+
  private:
   DISALLOW_COPY_AND_ASSIGN(UserWallpaperDelegate);
 };