message: Tidy up queue API and documentation.
  Reviewers: georgep
diff: @@ -260,7 +260,7 @@ void PoplarExecutor::ConnectInfeedsToStreamCallback(
  GetInfeedCopyHandle(infeed_info.stream_prefix, j),
  [&queue, length](void* dest) {
  tensorflow::TensorBuffer* buffer;
  - queue->Pop(buffer);
  + queue->BlockPop(buffer);
  std::memcpy(dest, buffer->data(), length);
  });
  }
  