anchor.diff:  }
   
   class AsyncBuildError extends BuildError {
  +  AsyncBuildError([String message]) : super(message);
  +
     Future<BuildError> resolve() => Future.value(this);
   }
   
  
positive.code: 
  Future<ElementDeclarationResult> _resolvedClassResult(Element element) async {
    var libraryElement = element.library;
    var libraryResult = await ResolvedLibraryResultImpl.tmp(libraryElement);
    if (libraryResult.state == ResultState.NOT_A_FILE) {
      // We don't have access to source information in summarized libraries,
  
negative.code: 
  class ErrorMessageForElement extends AsyncBuildError {
    final Element element;
  
    ErrorMessageForElement(this.element, String message) : super(message);
  
    @override
    Future<BuildError> resolve() =>
  