src/vs/base/common/cancellation.ts/CancellationTokenSource/cancel
class CancellationTokenSource:	cancel(): void {
		if (!this._token) {
			// save an object by returning the default
			// cancelled token when cancellation happens
			// before someone asks for the token
			this._token = CancellationToken.Cancelled;

		} else if (this._token instanceof MutableToken) {
			// actually cancel
			this._token.cancel();
		}
	}