Service worker playground

sw.js heartbeat_sw.js heartbeat_wait_until_sw.js install_error_sw.js blocking_install_error_sw.js activate_error_sw.js blocking_activate_error_sw.js message_error_sw.js blocking_message_error_sw.js fetch_error_sw.js blocking_fetch_error_sw.js sync_error_sw.js blocking_sync_error_sw.js sync_offline_sw.js