cros: Mount the existing eCryptfs vault to start migration.

chromeos/cryptohome/cryptohome_parameters.h

Index: chromeos/cryptohome/cryptohome_parameters.h
diff --git a/chromeos/cryptohome/cryptohome_parameters.h b/chromeos/cryptohome/cryptohome_parameters.h
index 7e60fc60c7968226b3693ea1be01a992d668ba4e..bf3d2904b4c9e7a5e826f9855404d690fc8e5318 100644
--- a/chromeos/cryptohome/cryptohome_parameters.h
+++ b/chromeos/cryptohome/cryptohome_parameters.h
@@ -170,6 +170,10 @@ class CHROMEOS_EXPORT MountParameters {
   // forces to use the new encryption. That is, makes it an error to mount
   // an existing home directory encrypted in the old way (ecryptfs).
   bool force_dircrypto_if_available = false;
+
+  // If |true|, mounts the existing ecryptfs vault to a temporary location while
+  // setting up a new dircrypto directory.
+  bool to_migrate_from_ecryptfs = false;
 };
 
 // This function returns true if cryptohome of |account_id| is migrated to