anchor.diff:  AnalysisBackend get analysisBackend => ss.lookup(#_analysisBackend);
   
   final Logger _logger = new Logger('pub.analyzer.backend');
  +
  +const Duration freshThreshold = const Duration(hours: 12);
  +const Duration obsoleteThreshold = const Duration(days: 180);
   
   /// Datastore-related access methods for the analyzer service
   class AnalysisBackend {
  
positive.code: 
      // Is latest analysis older than 4 hours?
      final DateTime now = new DateTime.now().toUtc();
      if (now.difference(versionAnalysis.analysisTimestamp).inHours < 4) {
        return false;
      }
  
  
negative.code:     }
  
      // Does package have analysis for the current version?
      final Key versionKey =
          packageKey.append(PackageVersionAnalysis, id: packageVersion);
      final PackageVersionAnalysis versionAnalysis =
          (await db.lookup([versionKey])).single;
      if (versionAnalysis == null) return true;
  
      // Is current analysis version newer?
  