function ThrottledCancellationToken(hostCancellationToken) {
            this.hostCancellationToken = hostCancellationToken;
            // Store when we last tried to cancel.  Checking cancellation can be expensive (as we have
            // to marshall over to the host layer).  So we only bother actually checking once enough
            // time has passed.
            this.lastCancellationCheckTime = 0;
        }
A cancellation that throttles calls to the host