anchor.diff:      snapshot = '$tmp/snapshot';
       env = Map<String, String>.from(e);
       env['DART_CONFIGURATION'] = tag;
  -    env['OPTIONS'] = extraFlags.join(' ');
  +    cmd = [precompiler] + extraFlags + [fileName, snapshot];
     }
   
     TestResult run() {
  -    TestResult result = runCommand([precompiler, fileName, snapshot], env);
  +    TestResult result = runCommand(cmd, env);
       if (result.exitCode != 0) {
         return result;
       }
  
positive.code:       this.fileName, List<String> extraFlags) {
      description = '$prefix-$tag';
      dart = '$top/out/$tag/dart';
      cmd = [dart, "--deterministic"] + extraFlags + [fileName];
    }
  
    TestResult run() {
  
negative.code:   String fileName;
    String snapshot;
    Map<String, String> env;
    List<String> cmd;
  }
  
  /// Concrete test runner of bytecode.
  