[cros] Add support for transparent background in sign in screen.

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 c4bdb9fcf7436bfff689dfb54990093564ec72ff..ff14ea94d48463f44f61f998dc412e856bfd824b 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1270,6 +1270,9 @@ const char kDisableGData[]                  = "disable-gdata";
 // Enables Libcros.
 const char kEnableLibcros[]                = "enable-libcros";
 
+// Enables new OOBE/sign in design.
+extern const char kEnableNewOobe[]         = "enable-new-oobe";
+
 // Enables touchpad three-finger-click as middle button.
 const char kEnableTouchpadThreeFingerClick[]
     = "touchpad-enable-three-finger-click";