anchor.diff:    final PerformanceLog _logger;
   
     /// The [FileSystem] to access file during compilation.
  -  final FileSystem _fileSystem;
  +  final front_end.FileSystem _fileSystem;
   
     /// The object that knows how to resolve "package:" and "dart:" URIs.
     final UriTranslator uriTranslator;
  
positive.code:   }
  }
  
  /// Adapter of [FileSystemState] to [FileSystem].
  class _FileSystemAdaptor implements FileSystem {
    final FileSystemState fsState;
    final pathos.Context pathContext;
  
    _FileSystemAdaptor(this.fsState, this.pathContext);
  
    @override
    FileSystemEntity entityForUri(Uri uri) {
      if (uri.isScheme('file')) {
        var path = pathContext.fromUri(uri);
        var file = fsState.getFileForPath(path);
        return new _FileSystemEntityAdaptor(uri, file);
      } else {
        throw new ArgumentError(
            'Only file:// URIs are supported, but $uri is given.');
      }
    }
  }
  
  /// Adapter of [FileState] to [FileSystemEntity].
  class _FileSystemEntityAdaptor implements FileSystemEntity {
    final Uri uri;
    final FileState file;
  
  
negative.code: import 'package:front_end/src/api_prototype/byte_store.dart';
  import 'package:front_end/src/api_prototype/compilation_message.dart';
  import 'package:front_end/src/api_prototype/compiler_options.dart';
  import 'package:front_end/src/api_prototype/file_system.dart' as front_end;
  import 'package:front_end/src/base/libraries_specification.dart';
  import 'package:front_end/src/base/performance_logger.dart';
  import 'package:front_end/src/base/processed_options.dart';
  