Return the summary metadata for the given tag on the given run.

    Args:
      run: A string name of the run for which summary metadata is to be
        retrieved.
      tag: A string name of the tag whose summary metadata is to be
        retrieved.

    Raises:
      KeyError: If the run is not found, or the tag is not available for
        the given run.

    Returns:
      A `SummaryMetadata` protobuf.

def SummaryMetadata(self, run, tag):
    """Return the summary metadata for the given tag on the given run.

    Args:
      run: A string name of the run for which summary metadata is to be
        retrieved.
      tag: A string name of the tag whose summary metadata is to be
        retrieved.

    Raises:
      KeyError: If the run is not found, or the tag is not available for
        the given run.

    Returns:
      A `SummaryMetadata` protobuf.
    """
    accumulator = self.GetAccumulator(run)
    return accumulator.SummaryMetadata(tag)