anchor.diff:    final Element element;
   
     HFieldAccess(this.element, List<HInstruction> inputs) : super(inputs);
  -
  -  bool isFromActivation() => element === null;
   }
   
   class HFieldGet extends HFieldAccess {
  
positive.code: class HFieldSet extends HFieldAccess {
    HFieldSet(Element element, HInstruction receiver, HInstruction value)
        : super(element, <HInstruction>[receiver, value]);
    HFieldSet.fromActivation(receiver, value)
        : this(null, receiver, value);
  
    HInstruction get receiver() => inputs[0];
    HInstruction get value() => inputs[1];
  
negative.code:   HFieldGet(Element element, HInstruction receiver,
              [this.isFinalOrConst = false])
        : super(element, <HInstruction>[receiver]);
  
    HInstruction get receiver() => inputs[0];
  
  