code: def GetMessages(self, formatter_mediator, event):
      
      if self.DATA_TYPE != event.data_type:
        raise errors.WrongFormatter('Unsupported data type: {0:s}.'.format(
            event.data_type))
  
      event_values = event.CopyToDict()
  
      primary_url = event_values['primary_url']
      secondary_url = event_values['secondary_url']
  
      # There is apparently a bug, either in GURL.cc or
      # content_settings_pattern.cc where URLs with file:// scheme are stored in
      # the URL as an empty string, which is later detected as being Invalid, and
      # Chrome produces the following example logs:
      # content_settings_pref.cc(469)] Invalid pattern strings: https://a.com:443,
      # content_settings_pref.cc(295)] Invalid pattern strings: ,
      # content_settings_pref.cc(295)] Invalid pattern strings: ,*
      # More research needed, could be related to https://crbug.com/132659
  
      if primary_url == '':
        subject = 'local file'
  
      elif secondary_url in (primary_url, '*'):
        subject = primary_url
  
      elif secondary_url == '':
        subject = '{0:s} embedded in local file'.format(primary_url)
  
      else:
        subject = '{0:s} embedded in {1:s}'.format(primary_url, secondary_url)
  
      event_values['subject'] = subject
  
      return self._ConditionalFormatMessages(event_values)
docs: Determines the formatted message strings for an event object.
  
      Args:
        formatter_mediator (FormatterMediator): mediates the interactions
            between formatters and other components, such as storage and Windows
            EventLog resources.
        event (EventObject): event.
  
      Returns:
        tuple(str, str): formatted message string and short message string.
  
      Raises:
        WrongFormatter: if the event object cannot be formatted by the formatter.