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

components/onc/onc_constants.h

Index: components/onc/onc_constants.h
diff --git a/components/onc/onc_constants.h b/components/onc/onc_constants.h
index 6329ff821af026aad76573744e1f662fb9d73227..e3b659451fd0b49a5d2fe5023777750229c03416 100644
--- a/components/onc/onc_constants.h
+++ b/components/onc/onc_constants.h
@@ -367,6 +367,10 @@ ONC_EXPORT extern const char kPassword[];
 ONC_EXPORT extern const char kPasswordAndOTP[];
 }  // openvpn_user_auth_type
 
+namespace third_party_vpn {
+ONC_EXPORT extern const char kExtensionID[];
+}  // third_party_vpn
+
 namespace verify_x509 {
 ONC_EXPORT extern const char kName[];
 ONC_EXPORT extern const char kType[];