anchor.diff:  /// any previously returned result, even inside of the same library.
   class AnalysisResult extends ResolvedUnitResultImpl {
     static final _UNCHANGED = new AnalysisResult(
  -      null, null, null, null, null, null, null, null, null, null, null, null);
  -
  -  /// The [SourceFactory] with which the file was analyzed.
  -  final SourceFactory sourceFactory;
  +      null, null, null, null, null, null, null, null, null, null, null);
   
     /// The signature of the result based on the content of the file, and the
     /// transitive closure of files imported and exported by the library of
  
positive.code:           resolvedUnits.add(
              new AnalysisResult(
                currentSession,
                _sourceFactory,
                unitFile.path,
                unitFile.uri,
                unitFile.exists,
  
negative.code:       this._index)
        : super(session, path, uri, exists, content, lineInfo, isPart, unit,
              errors);
  }
  
  class DriverPerformance {
  