Speed up custom wallpaper switching time and wallpaper manager code refactor

chrome/browser/chromeos/login/user.cc

Index: chrome/browser/chromeos/login/user.cc
diff --git a/chrome/browser/chromeos/login/user.cc b/chrome/browser/chromeos/login/user.cc
index ab451002f2114121a1b1243fa72f014356d2e3f1..afbb2740f17d2a7a86e790790a1f486851ea1c0a 100644
--- a/chrome/browser/chromeos/login/user.cc
+++ b/chrome/browser/chromeos/login/user.cc
@@ -67,10 +67,6 @@ void User::SetStubImage(int image_index) {
   image_is_stub_ = true;
 }
 
-void User::SetWallpaperThumbnail(const SkBitmap& wallpaper_thumbnail) {
-  wallpaper_thumbnail_ = wallpaper_thumbnail;
-}
-
 std::string User::GetAccountName(bool use_display_email) const {
   if (use_display_email && !display_email_.empty())
     return GetUserName(display_email_);