anchor.diff:    return result;
   }
   
  +/// Given an assetBase location and a flutter.yaml manifest, return a map of
  +/// assets to asset variants.
   Map<_Asset, List<_Asset>> _parseAssets(
     PackageMap packageMap,
     Map<String, dynamic> manifestDescriptor,
  -  String assetBase
  -) {
  +  String assetBase, {
  +  List<String> excludeDirs: const <String>[]
  +}) {
     Map<_Asset, List<_Asset>> result = <_Asset, List<_Asset>>{};
  +
     if (manifestDescriptor == null)
       return result;
  +
  +  excludeDirs = excludeDirs.map(
  +    (String exclude) => path.absolute(exclude) + Platform.pathSeparator).toList();
  +
     if (manifestDescriptor.containsKey('assets')) {
       for (String asset in manifestDescriptor['assets']) {
         _Asset baseAsset = _resolveAsset(packageMap, assetBase, asset);
  
positive.code:     zipBuilder.addEntry(assetEntry);
    }
  
    zipBuilder.addEntry(_createAssetManifest(assets));
  
    ZipEntry fontManifest = _createFontManifest(manifestDescriptor, usesMaterialDesign, includeRobotoFonts);
    if (fontManifest != null)
  
negative.code: }) async {
    printTrace('Building $outputPath');
  
    Map<_Asset, List<_Asset>> assetVariants = _parseAssets(
      new PackageMap(path.join(assetBasePath, '.packages')),
      manifestDescriptor,
      assetBasePath,
      excludeDirs: <String>[workingDirPath, path.join(assetBasePath, 'build')]
    );
  
    final bool usesMaterialDesign = manifestDescriptor != null &&
      manifestDescriptor['uses-material-design'] == true;
  
    ZipBuilder zipBuilder = new ZipBuilder();
  
    if (snapshotFile != null)
      zipBuilder.addEntry(new ZipEntry.fromFile(_kSnapshotKey, snapshotFile));
  
    for (_Asset asset in assetVariants.keys) {
      ZipEntry assetEntry = _createAssetEntry(asset);
      if (assetEntry == null)
        return 1;
      zipBuilder.addEntry(assetEntry);
  
      for (_Asset variant in assetVariants[asset]) {
        ZipEntry variantEntry = _createAssetEntry(variant);
        if (variantEntry == null)
          return 1;
  