anchor.diff:    ///
     /// Should be null in other cases.
     Expression initializer; // May be null.
  +
  +  /// If this is a formal parameter of a concrete method, its formal safety.
  +  /// Otherwise ignored.
  +  ///
  +  /// See [FormalSafety] for details.
  +  FormalSafety formalSafety = FormalSafety.safe;
  +
  +  /// If this is a formal parameter of a method, its interface safety.
  +  /// Otherwise ignored.
  +  ///
  +  /// See [InterfaceSafety] for details.
  +  InterfaceSafety interfaceSafety = InterfaceSafety.typed;
   
     VariableDeclaration(this.name,
         {this.initializer,
  
positive.code: class PropertyGet extends Expression {
    Expression receiver;
    Name name;
  
    Reference interfaceTargetReference;
  
  
negative.code:   Expression receiver;
    Name name;
    Arguments arguments;
    DispatchCategory dispatchCategory = DispatchCategory.dynamicDispatch;
  
    Reference interfaceTargetReference;
  
  