Iterator over all catapult trace events, as python values.

def _events(self):
    """Iterator over all catapult trace events, as python values."""
    for did, device in sorted(six.iteritems(self._proto.devices)):
      if device.name:
        yield dict(
            ph=_TYPE_METADATA,
            pid=did,
            name='process_name',
            args=dict(name=device.name))
      yield dict(
          ph=_TYPE_METADATA,
          pid=did,
          name='process_sort_index',
          args=dict(sort_index=did))
      for rid, resource in sorted(six.iteritems(device.resources)):
        if resource.name:
          yield dict(
              ph=_TYPE_METADATA,
              pid=did,
              tid=rid,
              name='thread_name',
              args=dict(name=resource.name))
        yield dict(
            ph=_TYPE_METADATA,
            pid=did,
            tid=rid,
            name='thread_sort_index',
            args=dict(sort_index=rid))
    # TODO(sammccall): filtering and downsampling?
    for event in self._proto.trace_events:
      yield self._event(event)