anchor.diff:      ],
       'causal-async-stacks': [
         _boolValues,
  -      _setSaneAsyncStacks,
  +      _setCausalAsyncStacks,
         (debugger, _) => debugger.saneAsyncStacks
       ],
  +    'awaiter-stacks': [
  +      _boolValues,
  +      _setAwaiterStacks,
  +      (debugger, _) => debugger.awaiterStacks
  +    ]
     };
   
     static Future _setBreakOnException(debugger, name, value) async {
  
positive.code:     debugger.console.print('${name} = ${value}');
    }
  
    static Future _setSaneAsyncStacks(debugger, name, value) async {
      if (value == 'true') {
        debugger.saneAsyncStacks = true;
      } else {
        debugger.saneAsyncStacks = false;
      }
      debugger.refreshStack();
      debugger.console.print('${name} = ${value}');
    }
  
    Future run(List<String> args) async {
  
negative.code:   void updateStackFrames(S.ServiceMap newStack) {
      List frameElements = _frameList.children;
      List newFrames;
      if (_debugger.awaiterStacks &&
          (newStack[ObservatoryDebugger.kAwaiterStackFrames] != null)) {
        newFrames = newStack[ObservatoryDebugger.kAwaiterStackFrames];
      } else if (_debugger.causalAsyncStacks &&
          (newStack[ObservatoryDebugger.kAsyncCausalStackFrames] != null)) {
        newFrames = newStack[ObservatoryDebugger.kAsyncCausalStackFrames];
      } else {
  