code: func (m *Mapping) string() string {
  	bits := ""
  	if m.HasFunctions {
  		bits = bits + "[FN]"
  	}
  	if m.HasFilenames {
  		bits = bits + "[FL]"
  	}
  	if m.HasLineNumbers {
  		bits = bits + "[LN]"
  	}
  	if m.HasInlineFrames {
  		bits = bits + "[IN]"
  	}
  	return fmt.Sprintf("%d: %#x/%#x/%#x %s %s %s",
  		m.ID,
  		m.Start, m.Limit, m.Offset,
  		m.File,
  		m.BuildID,
  		bits)
  }
docs: // string dumps a text representation of a mapping. Intended mainly
  // for debugging purposes.