cryptohome: Add dbus method and signal name for encryption migration.

chromeos/cryptohome/homedir_methods.h

Index: chromeos/cryptohome/homedir_methods.h
diff --git a/chromeos/cryptohome/homedir_methods.h b/chromeos/cryptohome/homedir_methods.h
index 2e54b74cdd5c0650f32b07dbc368d8e672711f7e..61b20b27f80ce6d822d6eaa05b267fa4045b5503 100644
--- a/chromeos/cryptohome/homedir_methods.h
+++ b/chromeos/cryptohome/homedir_methods.h
@@ -105,6 +105,12 @@ class CHROMEOS_EXPORT HomedirMethods {
       const Identification& id,
       const GetAccountDiskUsageCallback& callback) = 0;
 
+  // Asks cryptohomed to migrate the cryptohome to the new encryption method
+  // for the user specified by |id|, using |auth| to unlock the key.
+  virtual void MigrateToDircrypto(const Identification& id,
+                                  const Authorization& auth,
+                                  const Callback& callback) = 0;
+
   // Creates the global HomedirMethods instance.
   static void Initialize();