getChunkSize = function(id) {
            var fileState = handler._getFileState(id);

            if (fileState.chunkSize) {
                return fileState.chunkSize;
            }

            else {
                var chunkSize = chunking.partSize;

                if (qq.isFunction(chunkSize)) {
                    chunkSize = chunkSize(id, getSize(id));
                }

                fileState.chunkSize = chunkSize;
                return chunkSize;
            }
        }
Common API exposed to creators of XHR handlers.  This is reused and possibly overriding in some cases by specific
XHR upload handlers.

@constructor