anchor.diff:    @override
     void visitChildren(ElementVisitor visitor) =>
         throw unreachableError("visitChildren");
  +
  +  @override
  +  bool get isAlwaysThrows => throw unreachableError("isAlwaysThrows");
  +
  +  @override
  +  bool get isVisibleForTesting => throw unreachableError("isVisibleForTesting");
   }
   
   bool _isSetterName(String name) => name.endsWith("=");
  
positive.code:         return ec.subtypeQuantifyCapability;
        case "SuperclassQuantifyCapability":
          return new ec.SuperclassQuantifyCapability(
              constant.fields["upperBound"].toTypeValue().element,
              excludeUpperBound:
                  constant.fields["excludeUpperBound"].toBoolValue());
        case "TypeAnnotationQuantifyCapability":
          return new ec.TypeAnnotationQuantifyCapability(
              transitive: constant.fields["transitive"].toBoolValue());
        case "_CorrespondingSetterQuantifyCapability":
          return ec.correspondingSetterQuantifyCapability;
        case "_AdmitSubtypeCapability":
  
negative.code:             EvaluationResultImpl evaluation =
                  _annotationEvaluationResult(metadatum);
              if (evaluation?.value != null) {
                DartObject value = evaluation.value;
                Object metadataFieldValue =
                    value.getField("metadataType").toTypeValue().element;
                if (metadataFieldValue == null ||
                    value.getField("metadataType").type.element != typeClass) {
                  // TODO(sigurdm) implement: Create a span for the annotation.
                  _warn(
                      WarningKind.badMetadata,
                      "The metadata must be a Type. "
                      "Found ${value.getField("metadataType").type.element.name}",
                      import);
                  continue;
                }
                ClassElement reflector =
                    value.getField("(super)").getField("reflector").type.element;
                if (reflector == null ||
                    reflector.type.element.supertype.element !=
                        reflectableClass) {
  