Get index of runs and assets for a given plugin.

    Args:
      plugin_name: Name of the plugin we are checking for.

    Returns:
      A dictionary that maps from run_name to a list of plugin
        assets for that run.

def PluginAssets(self, plugin_name):
    """Get index of runs and assets for a given plugin.

    Args:
      plugin_name: Name of the plugin we are checking for.

    Returns:
      A dictionary that maps from run_name to a list of plugin
        assets for that run.
    """
    with self._accumulators_mutex:
      # To avoid nested locks, we construct a copy of the run-accumulator map
      items = list(six.iteritems(self._accumulators))

    return {run: accum.PluginAssets(plugin_name) for run, accum in items}