anchor.diff:  
     api.CompilerOutput get outputProvider => _outputProvider;
   
  -  Uri _mainLibraryUri;
  +  List<CodeLocation> _userCodeLocations = <CodeLocation>[];
   
     JClosedWorld backendClosedWorldForTesting;
   
  
positive.code:   }
  
    void compileFromKernel(Uri rootLibraryUri, Iterable<Uri> libraries) {
      selfTask.measureSubtask("compileFromKernel", () {
        JClosedWorld closedWorld = selfTask.measureSubtask("computeClosedWorld",
            () => computeClosedWorld(rootLibraryUri, libraries));
  
negative.code:     if (element == null) return assumeInUserCode;
      Uri libraryUri = _uriFromElement(element);
      if (libraryUri == null) return false;
      if (_userCodeLocations.isEmpty && assumeInUserCode) return true;
      return _userCodeLocations.any(
          (CodeLocation codeLocation) => codeLocation.inSameLocation(libraryUri));
    }
  
    /// Return a canonical URI for the source of [element].
  