anchor.diff:  }
   
   /// Shared state between delimited IrBuilders within the same function.
  -class IrBuilderSharedState {
  +class IrBuilderDelimitedState {
     final ConstantSystem constantSystem;
   
     /// A stack of collectors for breaks.
  
positive.code:       add(new ir.SetField(environment.lookup(location.box),
                            location.field,
                            initialValue));
      } else if (isInMutableVariable(variableElement)) {
        add(new ir.LetMutable(getMutableVariable(variableElement),
                              initialValue));
      } else {
        initialValue.useElementAsHint(variableElement);
        environment.extend(variableElement, initialValue);
  
negative.code:     for (LocalVariableElement variable in tryStatementInfo.boxedOnEntry) {
        assert(catchBuilder.isInMutableVariable(variable));
        ir.Primitive value = catchBuilder.buildLocalVariableGet(variable);
        // Note that we remove the variable from the set of mutable variables
        // here (and not above for the try body).  This is because the set of
        // mutable variables is global for the whole function and not local to
        // a delimited builder.
        catchBuilder.removeMutableVariable(variable);
        catchBuilder.environment.update(variable, value);
      }
  