anchor.diff:        : super(fileSystem, platformKernel, strongMode: strongMode);
   
     @override
  -  Future<Program> compile(Uri script) async {
  +  Future<Program> compileInternal(Uri script) async {
       return requireMain
           ? kernelForProgram(script, options)
           : kernelForBuildUnit([script], options..chaseDependencies = true);
  
positive.code:       };
    }
  
    Future<Program> compile(Uri script);
  }
  
  class IncrementalCompiler extends Compiler {
  
negative.code: 
    String toString() => "_CompilationCrash(${errorString})";
  }
  
  Future<T> runWithPrintToStderr<T>(Future<T> f()) {
    return runZoned(() => new Future<T>(f),
        zoneSpecification: new ZoneSpecification(
            print: (_1, _2, _3, String line) => stderr.writeln(line)));
  }
  