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

ash/accelerators/accelerator_controller.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/accelerators/accelerator_controller.h"
 
 #include "ash/accelerators/accelerator_table.h"
 #include "ash/ash_switches.h"
 #include "ash/caps_lock_delegate.h"
 #include "ash/desktop_background/desktop_background_controller.h"
@@ skipping 138 matching lines @@
   ash::Shell::GetPrimaryRootWindow()->layer()->GetAnimator()->StartAnimation(
       screen_rotation.release());
   return true;
 }
 
 bool HandleToggleDesktopBackgroundMode() {
   ash::DesktopBackgroundController* desktop_background_controller =
       ash::Shell::GetInstance()->desktop_background_controller();
   if (desktop_background_controller->desktop_background_mode() ==
       ash::DesktopBackgroundController::BACKGROUND_IMAGE) {
-    desktop_background_controller->SetDesktopBackgroundSolidColorMode();
+    desktop_background_controller->SetDesktopBackgroundSolidColorMode(
+        SK_ColorBLACK);
   } else {
     ash::Shell::GetInstance()->user_wallpaper_delegate()->
-        SetLoggedInUserWallpaper();
+        InitializeWallpaper();
   }
   return true;
 }
 
 bool HandleToggleRootWindowFullScreen() {
   ash::Shell::GetPrimaryRootWindow()->ToggleFullScreen();
   return true;
 }
 
 bool HandlePrintLayerHierarchy() {
@@ skipping 377 matching lines @@
     // Then set this one as active.
     Shell::GetInstance()->launcher()->ActivateLauncherItem(found_index);
   }
 }
 
 bool AcceleratorController::CanHandleAccelerators() const {
   return true;
 }
 
 }  // namespace ash