Enable user change background image in settings page in Aura build.

chrome/browser/chromeos/login/user_manager.h

Index: chrome/browser/chromeos/login/user_manager.h
diff --git a/chrome/browser/chromeos/login/user_manager.h b/chrome/browser/chromeos/login/user_manager.h
index 2f4f5e6013295e7c4cb99a5630022cb7c3c5473f..119f62b5aa0564dd6d12fccaf06eec510b5ca22a 100644
--- a/chrome/browser/chromeos/login/user_manager.h
+++ b/chrome/browser/chromeos/login/user_manager.h
@@ -37,6 +37,9 @@ class UserManager {
   // A vector pref of the users who have logged into the device.
   static const char kLoggedInUsers[];
 
+  // A dictionary that maps usernames to file paths to their wallpapers.
+  static const char kUserWallpapers[];
+
   // A dictionary that maps usernames to file paths to their images.
   static const char kUserImages[];
 
@@ -111,6 +114,17 @@ class UserManager {
   virtual std::string GetUserDisplayEmail(
       const std::string& username) const = 0;
 
+  // Returns the index of the default wallpapers saved in local state for user
+  // |username| if it is known (was previousely set by
+  // |SaveWallpaperToLocalState| call).
+  // Otherwise, returns default wallpaper index.
+  virtual int GetUserWallpaper(const std::string& username) = 0;
+
+  // Sets user wallpaper to the default wallpaper with index |wallpaper_index|,
+  // updates Local State.
+  virtual void SaveWallpaperDefaultIndex(const std::string& username,
+                                         int wallpaper_index) = 0;
+
   // Sets user image to the default image with index |image_index|, sends
   // LOGIN_USER_IMAGE_CHANGED notification and updates Local State.
   virtual void SaveUserDefaultImageIndex(const std::string& username,