message: change get_metadata_buffer functions from internal api to public api in metadata.
diff: @@ -348,7 +348,7 @@ class MetadataPopulator(object):
  associated files.
  """
  # Load the model metadata from src_model_buf if exist.
  - metadata_buffer = _get_metadata_buffer(src_model_buf)
  + metadata_buffer = get_metadata_buffer(src_model_buf)
  if metadata_buffer:
  self.load_metadata_buffer(metadata_buffer)
  @@ -730,7 +730,7 @@ class MetadataDisplayer(object):
  """
  if not model_buffer:
  raise ValueError("model_buffer cannot be empty.")
  - metadata_buffer = _get_metadata_buffer(model_buffer)
  + metadata_buffer = get_metadata_buffer(model_buffer)
  if not metadata_buffer:
  raise ValueError("The model does not have metadata.")
  associated_file_list = cls._parse_packed_associted_file_list(model_buffer)
  @@ -843,7 +843,7 @@ def _assert_metadata_buffer_identifier(metadata_buf):
  " be a valid TFLite Metadata.")
  -def _get_metadata_buffer(model_buf):
  +def get_metadata_buffer(model_buf):
  """Returns the metadata in the model file as a buffer.
  Args:
  