anchor.diff:      LibraryUpdater,
       Logger;
   
  +import 'package:compiler/implementation/js/js.dart' as jsAst;
  +
   part 'caching_compiler.dart';
   
   const List<String> INCREMENTAL_OPTIONS = const <String>[
  
positive.code:       if (compiler.compilationFailed) {
          return null;
        } else {
          return updater.computeUpdateJs();
        }
      });
    }
  }
  
negative.code:   final List<String> options;
    final CompilerOutputProvider outputProvider;
    final Map<String, dynamic> environment;
    final List<String> _updates = <String>[];
  
    Compiler _compiler;
  
  