src/vs/platform/log/common/log.ts/AbstractLoggerService/constructor
class AbstractLoggerService:	constructor(
		private logLevel: LogLevel,
		onDidChangeLogLevel: Event<LogLevel>,
	) {
		super();
		this._register(onDidChangeLogLevel(logLevel => {
			this.logLevel = logLevel;
			this.logLevelChangeableLoggers.forEach(logger => logger.setLevel(logLevel));
		}));
	}