checkToCreateResponseInfo_ = function() {
      'use strict';
      if (++numChunksSent == numChunksToSend) {
        goog.net.CrossDomainRpc.createResponseInfo_(
            dummyUri, numChunksToSend, isDataJson, status, headers);
      }
    }
Makes response available for grandparent (requester)'s receiveResponse
call to pick up by creating a series of iframes pointed to the dummy URI
with a payload (value after either ? or #) carrying a chunk of response
data and a response info iframe that tells the grandparent (requester) the
readiness of response.
@param {string} data Response data (string or JSON string).
@param {boolean} isDataJson true if data is a JSON string; false if just a
    string.
@param {Object} echo Parameters to echo back
    "xdpe:request-id": Server that produces the response needs to
    copy it here to support multiple current XD requests on the same page.
    "xdpe:dummy-uri": URI to a dummy resource that response
    iframes point to to gain the domain of the client.  This can be an
    image (IE) or a CSS file (FF) found on the requester's page.
    Server should copy value from request parameter "xdpe:dummy-uri".
@param {number} status HTTP response status code.
@param {string} headers Response headers in JSON format.