code: def scalars_route(self, request):
      
      # TODO: return HTTP status code for malformed requests
      tag_regex_string = request.args.get('tag')
      run = request.args.get('run')
      mime_type = 'application/json'
  
      try:
        body = self.scalars_impl(run, tag_regex_string)
      except ValueError as e:
        return http_util.Respond(
            request=request,
            content=str(e),
            content_type='text/plain',
            code=500)
  
      # Produce the response.
      return http_util.Respond(request, body, mime_type)
docs: Given a tag regex and single run, return ScalarEvents.
  
      This route takes 2 GET params:
      run: A run string to find tags for.
      tag: A string that is a regex used to find matching tags.
      The response is a JSON object:
      {
        // Whether the regular expression is valid. Also false if empty.
        regexValid: boolean,
  
        // An object mapping tag name to a list of ScalarEvents.
        payload: Object<string, ScalarEvent[]>,
      }