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