Load GraphDef from a binary proto file.

def _load_graphdef_protobuf(handle, **kwargs):
    """Load GraphDef from a binary proto file."""
    # as_graph_def
    graph_def = tf.GraphDef.FromString(handle.read())

    # check if this is a lucid-saved model
    # metadata = modelzoo.util.extract_metadata(graph_def)
    # if metadata is not None:
    #   url = handle.name
    #   return modelzoo.vision_base.Model.load_from_metadata(url, metadata)

    # else return a normal graph_def
    return graph_def