anchor.diff:      genSnapshot,
       '--vm_isolate_snapshot=$vmIsolateSnapshot',
       '--isolate_snapshot=$isolateSnapshot',
  -    '--package_root=$packagesPath',
  +    '--packages=${packageMap.packagesPath}',
       '--url_mapping=dart:mojo.internal,$mojoInternalPath',
       '--url_mapping=dart:ui,$uiPath',
       '--url_mapping=dart:jni,$jniPath',
  
positive.code:   }
  }
  
  String _getSdkExtensionPath(String packagesPath, String package) {
    Directory packageDir = new Directory(path.join(packagesPath, package));
    return path.dirname(packageDir.resolveSymbolicLinksSync());
  }
  
  /// Build an AOT snapshot. Return `null` (and log to `printError`) if the method
  
negative.code:   String vmEntryPoints = path.join(entryPointsDir, 'dart_vm_entry_points.txt');
    String ioEntryPoints = path.join(dartEntryPointsDir, 'dart_io_entries.txt');
  
    PackageMap packageMap = new PackageMap(PackageMap.globalPackagesPath);
    String packageMapError = packageMap.checkValid();
    if (packageMapError != null) {
      printError(packageMapError);
      return null;
    }
  
    String mojoPkg = _getSdkExtensionPath(packageMap, 'mojo');
    String mojoInternalPath = path.join(mojoPkg, 'sdk_ext', 'internal.dart');
  
    String skyEnginePkg = _getSdkExtensionPath(packageMap, 'sky_engine');
    String uiPath = path.join(skyEnginePkg, 'dart_ui', 'ui.dart');
    String jniPath = path.join(skyEnginePkg, 'dart_jni', 'jni.dart');
    String vmServicePath = path.join(skyEnginePkg, 'sdk_ext', 'dart', 'runtime', 'bin', 'vmservice', 'vmservice_io.dart');
  