[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 c73fd822a764c9fd1403681aac9562c99591e217..66c0b513de80636b5c0296d197b160eb12a69063 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1263,6 +1263,9 @@ 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";