anchor.diff:    TargetPlatform platform,
     BuildMode buildMode,
     String manifest,
  -  String resources
  +  String resources,
  +  Map<String, File> extraFiles
   ) async {
     _ApkComponents components = new _ApkComponents();
     components.manifest = new File(manifest);
     components.resources = resources == null ? null : new Directory(resources);
  +  components.extraFiles = extraFiles != null ? extraFiles : <String, File>{};
   
     if (tools.isLocalEngine) {
       String abiDir = platform == TargetPlatform.android_arm ? 'armeabi-v7a' : 'x86_64';
  
positive.code: 
    List<File> allFiles = <File>[
      components.manifest, components.icuData, components.libSkyShell, components.debugKeystore
    ]..addAll(components.jars);
  
    for (File file in allFiles) {
      if (!file.existsSync()) {
  
negative.code:       resources = _kDefaultResourcesPath;
    }
  
    _ApkComponents components = await _findApkComponents(platform, buildMode, manifest, resources, extraFiles);
  
    if (components == null) {
      printError('Failure building APK: unable to find components.');
  