anchor.diff:        sourcesList.forEach((s) => changeSet.removedSource(s));
         _resolver.clear();
         _context.applyChanges(changeSet);
  -      _context.performAnalysisTask();
  +      _ensureAnalysisDone(_context, _MAX_ANALYSIS_DURATION);
   
         return new Future.value(new AnalysisResults(
             issues, packageImports.toList(), resolvedImports));
  
positive.code: 
  Logger _logger = new Logger('analyzer');
  
  class MemoryResolver extends UriResolver {
    Map<String, Source> sources = {};
  
  
negative.code:       ChangeSet changeSet = new ChangeSet();
        sourcesList.forEach((s) => changeSet.addedSource(s));
        _context.applyChanges(changeSet);
        _ensureAnalysisDone(_context, _MAX_ANALYSIS_DURATION);
  
        List<AnalysisErrorInfo> errorInfos = [];
        sourcesList.forEach((s) {
  