Add an ONC property for the third-party VPN provider extension ID

chromeos/network/onc/onc_validator.h

Index: chromeos/network/onc/onc_validator.h
diff --git a/chromeos/network/onc/onc_validator.h b/chromeos/network/onc/onc_validator.h
index b535f9f26abe67308d7b9429c47e5bce72ecb74a..424f7ebe65edbaa8f1383cc96cd21ccd775d53c4 100644
--- a/chromeos/network/onc/onc_validator.h
+++ b/chromeos/network/onc/onc_validator.h
@@ -160,6 +160,7 @@ class CHROMEOS_EXPORT Validator : public Mapper {
   bool ValidateVPN(base::DictionaryValue* result);
   bool ValidateIPsec(base::DictionaryValue* result);
   bool ValidateOpenVPN(base::DictionaryValue* result);
+  bool ValidateThirdPartyVPN(base::DictionaryValue* result);
   bool ValidateVerifyX509(base::DictionaryValue* result);
   bool ValidateCertificatePattern(base::DictionaryValue* result);
   bool ValidateProxySettings(base::DictionaryValue* result);