anchor.diff:    chrome.DirectoryEntry root;
     ObjectStore store;
     Function progress;
  +  String branchName;
   
     Fetch(this.options){
       root = options.root;
       store = options.store;
       progress = options.progressCallback;
  +    branchName = options.branchName == null ? 'master' : options.branchName;
   
       if (progress == null) progress = nopFunction;
     }
  
positive.code: import 'package:chrome/chrome_app.dart' as chrome;
  
  import '../constants.dart';
  import '../fast_sha.dart';
  import '../file_operations.dart';
  import '../http_fetcher.dart';
  
negative.code:       return store.getCommitGraph([sha], 32).then((CommitGraph graph) {
          List<String> haveRefs = graph.commits.map((CommitObject commit)
              => commit.treeSha).toList();
          if (haveRefs.isEmpty) {
            haveRefs = null;
          }
          return fetcher.fetchRef([wantRef.sha], haveRefs, store.config.shallow,
              null, graph.nextLevel, null, progress).then((PackParseResult result) {
            List<int> packSha = result.data.sublist(result.data.length - 20);
  