Enable wallpaper boot animation for boot into sign in too. Add flag to disable it.

ash/desktop_background/desktop_background_controller.h

 // 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.
 
 #ifndef ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_
 #define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_
 
 #include "ash/ash_export.h"
 #include "ash/desktop_background/desktop_background_resources.h"
 #include "ash/wm/window_animations.h"
@@ skipping 22 matching lines @@
 
   // Opens the set wallpaper page in the browser.
   virtual void OpenSetWallpaperPage() = 0;
 
   // Returns true if user can open set wallpaper page. Only guest user returns
   // false currently.
   virtual bool CanOpenSetWallpaperPage() = 0;
 
   // Notifies delegate that wallpaper animation has finished.
   virtual void OnWallpaperAnimationFinished() = 0;
+
+  // Notifies delegate that wallpaper boot animation has finished.
+  virtual void OnWallpaperBootAnimationFinished() = 0;
 };
 
 // Loads selected desktop wallpaper from file system asynchronously and updates
 // background layer if loaded successfully.
 class ASH_EXPORT DesktopBackgroundController {
  public:
   enum BackgroundMode {
     BACKGROUND_IMAGE,
     BACKGROUND_SOLID_COLOR
   };
@@ skipping 70 matching lines @@
   scoped_refptr<WallpaperOperation> wallpaper_op_;
 
   base::WeakPtrFactory<DesktopBackgroundController> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_