anchor.diff:    final CompilerMessageConsumer consumer;
     String boundaryKey;
     Completer<CompilerOutput> compilerOutput;
  +
  +  bool _suppressCompilerMessages;
   
     void handler(String string) {
       const String kResultPrefix = 'result ';
  
positive.code:           string.substring(boundaryKey.length + 1, spaceDelimiter),
            int.parse(string.substring(spaceDelimiter + 1).trim())));
      }
      else
        consumer('compiler message: $string');
    }
  
    // This is needed to get ready to process next compilation result output,
    // with its own boundary key and new completer.
    void reset() {
      boundaryKey = null;
      compilerOutput = new Completer<CompilerOutput>();
    }
  }
  
  
negative.code: 
    Future<CompilerOutput> _compileExpression(
        _CompileExpressionRequest request) async {
      _stdoutHandler.reset(suppressCompilerMessages: true);
  
      // 'compile-expression' should be invoked after compiler has been started,
      // program was compiled.
  