anchor.diff:  
       // Modify a flag.
       var params = {
  -      'name' : 'code_comments',
  +      'name' : 'trace_isolates',
         'value' : 'true',
       };
       result = await vm.invokeRpcNoUpgrade('setFlag', params);
  
positive.code:     expect(result['unmodifiedFlags'].length, isPositive);
      bool found = false;
      for (var flag in result['unmodifiedFlags']) {
        if (flag['name'] == 'code_comments') {
          found = true;
          expect(flag['flagType'], equals('bool'));
          expect(flag['valueAsString'], equals('false'));
  
negative.code:   (VM vm) async {
      // Modify a flag.
      var params = {
        'name' : 'trace_isolates',
        'value' : '123',
      };
      var result = await vm.invokeRpcNoUpgrade('setFlag', params);
  