def PluginRunToTagToContent(self, plugin_name):
    """Returns a 2-layer dictionary of the form {run: {tag: content}}.

    The `content` referred above is the content field of the PluginData proto
    for the specified plugin within a Summary.Value proto.

    Args:
      plugin_name: The name of the plugin for which to fetch content.

    Returns:
      A dictionary of the form {run: {tag: content}}.
    """
    mapping = {}
    for run in self.Runs():
      try:
        tag_to_content = self.GetAccumulator(run).PluginTagToContent(
            plugin_name)
      except KeyError:
        # This run lacks content for the plugin. Try the next run.
        continue
      mapping[run] = tag_to_content
    return mapping