code: def SummaryMetadata(self, run, tag):
      
      accumulator = self.GetAccumulator(run)
      return accumulator.SummaryMetadata(tag)
docs: 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.