anchor.diff:    }
   
     @override
  -  MemberElement get memberContext => box.executableContext.memberContext;
  +  MemberElement get memberContext => box.memberContext;
   
     @override
     List<FunctionElement> get nestedClosures => const <FunctionElement>[];
  
positive.code: /// fields.
  class BoxLocal extends Local {
    final String name;
    final ExecutableElement executableContext;
  
    final int hashCode = _nextHashCode = (_nextHashCode + 10007).toUnsigned(30);
    static int _nextHashCode = 0;
  
    BoxLocal(this.name, this.executableContext);
  
    @override
    MemberElement get memberContext => executableContext.memberContext;
  
    String toString() => 'BoxLocal($name)';
  }
  
negative.code:         if (box == null) {
            // TODO(floitsch): construct better box names.
            String boxName = getBoxFieldName(closureFieldCounter++);
            box = new BoxLocal(
                boxName, executableContext, executableContext.memberContext);
          }
          String elementName = variable.name;
          String boxedName =
  