constructor(batchResponse, subRequests) {
        if (!batchResponse || !batchResponse.contentType) {
            // In special case(reported), server may return invalid content-type which could not be parsed.
            throw new RangeError("batchResponse is malformed or doesn't contain valid content-type.");
        }
        if (!subRequests || subRequests.size === 0) {
            // This should be prevent during coding.
            throw new RangeError("Invalid state: subRequests is not provided or size is 0.");
        }
        this.batchResponse = batchResponse;
        this.subRequests = subRequests;
        this.responseBatchBoundary = this.batchResponse.contentType.split("=")[1];
        this.perResponsePrefix = `--${this.responseBatchBoundary}${HTTP_LINE_ENDING}`;
        this.batchResponseEnding = `--${this.responseBatchBoundary}--`;
    }
Util class for parsing batch response.