Fix node build.

src/node/ext/call_credentials.h

@@ -75,9 +75,12 @@ typedef struct plugin_state {
   uv_async_t plugin_async;
 } plugin_state;
 
-void plugin_get_metadata(void *state, grpc_auth_metadata_context context,
-                         grpc_credentials_plugin_metadata_cb cb,
-                         void *user_data);
+int plugin_get_metadata(
+    void *state, grpc_auth_metadata_context context,
+    grpc_credentials_plugin_metadata_cb cb, void *user_data,
+    grpc_metadata creds_md[GRPC_METADATA_CREDENTIALS_PLUGIN_SYNC_MAX],
+    size_t *num_creds_md, grpc_status_code *status,
+    const char **error_details);
 
 void plugin_destroy_state(void *state);