anchor.diff:      final List<KernelTypeBuilder> interfaces = this.interfaces;
       if (interfaces != null) {
         for (int i = 0; i < interfaces.length; i++) {
  -        KernelNamedTypeBuilder interface = interfaces[i];
  +        KernelTypeBuilder interface = interfaces[i];
           result.add(interface.declaration);
         }
       }
  -    final KernelNamedTypeBuilder mixedInType = this.mixedInType;
  +    final KernelTypeBuilder mixedInType = this.mixedInType;
       if (mixedInType != null) {
         result.add(mixedInType.declaration);
       }
  
positive.code: 
    List<Declaration> computeDirectSupertypes(ClassBuilder objectClass) {
      final List<Declaration> result = <Declaration>[];
      final KernelNamedTypeBuilder supertype = this.supertype;
      if (supertype != null) {
        result.add(supertype.declaration);
      } else if (objectClass != this) {
  
negative.code:           fileUri);
        actualCls.supertype = null;
      }
      if (actualCls.supertype == null && supertype is! KernelNamedTypeBuilder) {
        supertype = null;
      }
      mixedInType = checkSupertype(mixedInType);
      actualCls.mixedInType =
          mixedInType?.buildMixedInType(library, charOffset, fileUri);
      if (actualCls.mixedInType == null &&
          mixedInType is! KernelNamedTypeBuilder) {
        mixedInType = null;
      }
      actualCls.isMixinDeclaration = isMixinDeclaration;
      // TODO(ahe): If `cls.supertype` is null, and this isn't Object, report a
      // compile-time error.
  