Speed up custom wallpaper switching time and wallpaper manager code refactor

chrome/browser/chromeos/login/user.h

Index: chrome/browser/chromeos/login/user.h
diff --git a/chrome/browser/chromeos/login/user.h b/chrome/browser/chromeos/login/user.h
index cd9a23fdcf2a6834552eb36e1e630c534810ca6e..2495aea28b5f966e1ff2fe4bd0d41241737c72f6 100644
--- a/chrome/browser/chromeos/login/user.h
+++ b/chrome/browser/chromeos/login/user.h
@@ -80,9 +80,6 @@ class User {
   // image has a URL, for other images empty URL is returned.
   GURL image_url() const { return user_image_.url(); }
 
-  // The thumbnail of user custom wallpaper.
-  const SkBitmap& wallpaper_thumbnail() const { return wallpaper_thumbnail_; }
-
   // True if user image is a stub (while real image is being loaded from file).
   bool image_is_stub() const { return image_is_stub_; }
 
@@ -137,7 +134,6 @@ class User {
   std::string display_email_;
   UserImage user_image_;
   OAuthTokenStatus oauth_token_status_;
-  SkBitmap wallpaper_thumbnail_;
 
   // Either index of a default image for the user, |kExternalImageIndex| or
   // |kProfileImageIndex|.