anchor.diff:        _fs.memory.entityForUri(uri).writeAsStringSync(contents);
   }
   
  +ByteStore createByteStore(String cachePolicy, String path) {
  +  switch (cachePolicy) {
  +    case 'memory':
  +      return new MemoryByteStore();
  +    case 'protected':
  +      return new ProtectedFileByteStore(path);
  +    case 'evicting':
  +      return new MemoryCachingByteStore(
  +          new EvictingFileByteStore(path, 1024 * 1024 * 1024 /* 1G */),
  +          64 * 1024 * 1024 /* 64M */);
  +    default:
  +      throw new UnsupportedError('Unknown cache policy: $cachePolicy');
  +  }
  +}
  +
   /// A string replacement edit in a source file.
   class Edit {
     final Uri uri;
  
positive.code:   }
  
    var dir = Directory.systemTemp.createTempSync('ikg-cache');
    compilerOptions.byteStore = new ProtectedFileByteStore(dir.path);
  
    var timer1 = new Stopwatch()..start();
    var generator =
  
negative.code: import 'dart:io' hide FileSystemEntity;
  
  import 'package:args/args.dart';
  import 'package:front_end/byte_store.dart';
  import 'package:front_end/file_system.dart' show FileSystemEntity;
  import 'package:front_end/front_end.dart';
  import 'package:front_end/incremental_kernel_generator.dart';
  import 'package:front_end/memory_file_system.dart';
  import 'package:front_end/physical_file_system.dart';
  import 'package:front_end/src/byte_store/protected_file_byte_store.dart';
  import 'package:kernel/target/flutter.dart';
  import 'package:kernel/target/targets.dart';
  
  