cros: Implement cryptohome backend for pin.

chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h

Index: chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
diff --git a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
index 933ca0e7920c77f668f5527f72d6bfe556bfe954..e4c813f762bad50e40cc7d1babee1798fc8ad2b4 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
@@ -351,6 +351,11 @@ class SigninScreenHandler
 
   // Enable or disable the pin keyboard for the given account.
   void UpdatePinKeyboardState(const AccountId& account_id);
+  void UpdatePinKeyboardStateCallback(const AccountId& account_id,
+                                      bool is_enabled);
+  // Callback run by PinBackend. If |should_enabled| is true the PIN keyboard is
+  // preloaded.
+  void PreloadPinKeyboardCallback(bool should_enabled);
 
   // WebUI message handlers.
   void HandleGetUsers();