xmlHttpPost(uri, postData, decodeChunks) {
    this.channelDebug_.debug(`---> POST: ${uri}, ${postData}, ${decodeChunks}`);
    this.postData_ = postData;
    this.requestStartTime_ = Date.now();
  }
@param {?Uri} uri The uri of the request.
@param {?string} postData The data for the post body.
@param {boolean} decodeChunks Whether to the result is expected to be
    encoded for chunking and thus requires decoding.