anchor.diff:    _checkIndividualOverridesFromClass(ClassDeclaration node,
         InterfaceType baseType, Set<String> seen, bool isSubclass) {
       for (var member in node.members) {
  -      if (member is ConstructorDeclaration) continue;
         if (member is FieldDeclaration) {
           if (member.isStatic) continue;
           for (var variable in member.fields.variables) {
  
positive.code:       // supertype of it, do an implicit downcast to Iterable<dynamic>. Then
        // we'll do a separate cast of the dynamic element to the variable's type.
        if (elementType == null) {
          var sequenceType = sequenceInterface.instantiate([DynamicTypeImpl.instance]);
  
          if (rules.isSubtypeOf(sequenceType, iterableType)) {
            _recordMessage(DownCast.create(
  
negative.code:     }
    }
  
    /// Records a [DownCast] of [expr] from [from] to [to], if there is one.
    ///
    /// If [from] is omitted, uses the static type of [expr].
  