Use a #fefefe solid color wallpaper background before user login for GAIA login flow

chrome/browser/chromeos/login/mock_user_manager.h

Index: chrome/browser/chromeos/login/mock_user_manager.h
diff --git a/chrome/browser/chromeos/login/mock_user_manager.h b/chrome/browser/chromeos/login/mock_user_manager.h
index 295028b33102b73115d11aa1a129a4f6feda4bf9..804c2da417f5bdbd327ec18bdd96e89cf12bfb9d 100644
--- a/chrome/browser/chromeos/login/mock_user_manager.h
+++ b/chrome/browser/chromeos/login/mock_user_manager.h
@@ -24,7 +24,7 @@ class MockUserManager : public UserManager {
   MOCK_METHOD0(DemoUserLoggedIn, void(void));
   MOCK_METHOD0(GuestUserLoggedIn, void(void));
   MOCK_METHOD1(EphemeralUserLoggedIn, void(const std::string&));
-  MOCK_METHOD0(SetLoggedInUserWallpaper, void(void));
+  MOCK_METHOD0(InitializeWallpaper, void(void));
   MOCK_METHOD1(UserSelected, void(const std::string&));
   MOCK_METHOD0(SessionStarted, void(void));
   MOCK_METHOD2(RemoveUser, void(const std::string&, RemoveUserDelegate*));