code: def _serve_image_metadata(self, request):
      
      tag = request.args.get('tag')
      run = request.args.get('run')
      sample = int(request.args.get('sample', 0))
      response = self._image_response_for_run(run, tag, sample)
      return http_util.Respond(request, response, 'application/json')
docs: Given a tag and list of runs, serve a list of metadata for images.
  
      Note that the images themselves are not sent; instead, we respond with URLs
      to the images. The frontend should treat these URLs as opaque and should not
      try to parse information about them or generate them itself, as the format
      may change.
  
      Args:
        request: A werkzeug.wrappers.Request object.
  
      Returns:
        A werkzeug.Response application.