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

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 77dfee8e2d38555aa9c7621485ddbcd7dcb64c6c..3b305b6b744c8d62b4391e22ffca3044756a046a 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1337,6 +1337,9 @@ const char kTabletUI[]                      = "tablet-ui";
 #endif
 
 #if defined(OS_CHROMEOS)
+// Disables wallpaper boot animation (except of OOBE case).
+const char kDisableBootAnimation[]          = "disable-boot-animation";
+
 // Disables gdata content provider.
 const char kDisableGData[]                  = "disable-gdata";