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

chrome/common/chrome_switches.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.
 
 // Defines all the command-line switches used by Chrome.
 
 #ifndef CHROME_COMMON_CHROME_SWITCHES_H_
 #define CHROME_COMMON_CHROME_SWITCHES_H_
 
 #include "build/build_config.h"
@@ skipping 346 matching lines @@
 extern const char kWindowPosition[];
 extern const char kWindowSize[];
 extern const char kWinHttpProxyResolver[];
 
 #if defined(OS_ANDROID)
 extern const char kTabletUI[];
 #endif
 
 #if defined(OS_CHROMEOS)
 // Keep switches in alphabetical order.
+extern const char kDisableBootAnimation[];
 extern const char kDisableGData[];
 extern const char kDisableHtml5Camera[];
 extern const char kDisableNewOobe[];
 extern const char kEnableTouchpadThreeFingerClick[];
 extern const char kSkipOAuthLogin[];
 extern const char kEnableDevicePolicy[];
 extern const char kEnableDriveV2Api[];
 extern const char kEnableGView[];
 extern const char kEnableKioskMode[];
 extern const char kEnableONCPolicy[];
@@ skipping 58 matching lines @@
 #else
 extern const char kEnablePrintPreview[];
 #endif
 
 // DON'T ADD RANDOM STUFF HERE. Put it in the main section above in
 // alphabetical order, or in one of the ifdefs (also in order in each section).
 
 }  // namespace switches
 
 #endif  // CHROME_COMMON_CHROME_SWITCHES_H_