[WebKit 537.36 (linux 0.0.0)] UserSignalMechanism User Signal Mechanism API [WebKit 537.36 (linux 0.0.0)] UserSignalMechanism User Signal Mechanism API provides __uspapi global provides __uspapi global implements ping command implements ping command implements getUSPData command implements getUSPData command sets cookies sets cookies cleans up after uninstall cleans up after uninstall