anchor.diff:        command.add('--ipv6');
       if (bundlePath != null) {
         command.add('--flutter-assets-dir=$bundlePath');
  +    }
  +    if (strongMode) {
  +      command.add('--strong');
       }
       command.addAll(<String>[
         '--enable-dart-profiling',
  
positive.code:     String bundlePath,
      bool enableObservatory: false,
      bool startPaused: false,
      int observatoryPort,
    }) {
      assert(executable != null); // Please provide the path to the shell in the SKY_SHELL environment variable.
  
negative.code:       // Start the engine subprocess.
        printTrace('test $ourTestCount: starting shell process${previewDart2? " in preview-dart-2 mode":""}');
  
        String mainDart = listenerFile.path;
        String bundlePath;
        bool strongMode = false;
  
        if (previewDart2) {
          mainDart = await compile(
            sdkRoot: artifacts.getArtifactPath(Artifact.flutterPatchedSdkPath),
            incrementalCompilerByteStorePath: '' /* not null is enough */,
            mainPath: listenerFile.path,
            packagesPath: PackageMap.globalPackagesPath,
            strongMode: true,
          );
  
          // bundlePath needs to point to a folder with `platform.dill` file.
          final Directory tempBundleDirectory = fs.systemTempDirectory
              .createTempSync('flutter_bundle_directory');
          finalizers.add(() async {
            printTrace('test $ourTestCount: deleting temporary bundle directory');
            temporaryDirectory.deleteSync(recursive: true);
          });
  
          // copy 'vm_platform_strong.dill' into 'platform.dill'
          final File vmPlatformStrongDill = fs.file(
              artifacts.getArtifactPath(Artifact.platformKernelStrongDill));
          final File platformDill = vmPlatformStrongDill.copySync(
              tempBundleDirectory.childFile('platform.dill').path);
          if (!platformDill.existsSync()) {
            printError('unexpected error copying platform kernel file');
          }
  
          bundlePath = tempBundleDirectory.path;
          strongMode = true;
        }
  
        final Process process = await _startProcess(
          shellPath,
  