code: func mergeBuildIntoAnnotation(c context.Context, step *miloProto.Step, build *buildbot.Build) error {
  	allProps := stringset.New(len(step.Property) + len(build.Properties))
  	for _, prop := range step.Property {
  		allProps.Add(prop.Name)
  	}
  	for _, prop := range build.Properties {
  		// Annotation protobuf overrides BuildBot properties.
  		if allProps.Has(prop.Name) {
  			continue
  		}
  		allProps.Add(prop.Name)
  
  		step.Property = append(step.Property, &miloProto.Step_Property{
  			Name:  prop.Name,
  			Value: fmt.Sprintf("%v", prop.Value),
  		})
  	}
  
  	return nil
  }
docs: // mergeBuildInfoIntoAnnotation merges BuildBot-specific build informtion into
  // a LogDog annotation protobuf.
  //
  // This consists of augmenting the Step's properties with BuildBot's properties,
  // favoring the Step's version of the properties if there are two with the same
  // name.