message: Make helper function global so it can be pickled.
  Fixes Windows tests after CL/257051579.
diff: @@ -443,6 +443,10 @@ class TFRecordIteratorTest(TFCompressionTestCase):
  for _ in tf_record.tf_record_iterator(fn_truncated):
  pass
  +def ChildProcess(writer, rs):
  + for r in rs:
  + writer.write(r)
  + writer.flush()
  class TFRecordWriterCloseAndFlushTests(test.TestCase):
  """TFRecordWriter close and flush tests"""
  @@ -481,13 +485,8 @@ class TFRecordWriterCloseAndFlushTests(test.TestCase):
  """test Flush"""
  records = list(map(self._Record, range(self._num_records)))
  - def childProcess(writer, rs):
  - for r in rs:
  - writer.write(r)
  - writer.flush()
  -
  write_process = multiprocessing.Process(
  - target=childProcess, args=(self._writer, records))
  + target=ChildProcess, args=(self._writer, records))
  write_process.start()
  write_process.join()
  actual = list(tf_record.tf_record_iterator(self._fn, self._options))
  