anchor.diff:     * Return `true` if errors should be produced for the given [source]. The
      * [entry] associated with the source is passed in for efficiency.
      */
  -  bool _shouldErrorsBeAnalyzed(Source source, cache.CacheEntry entry) {
  +  bool _shouldErrorsBeAnalyzed(Source source, CacheEntry entry) {
       if (source.isInSystemLibrary) {
         return _options.generateSdkErrors;
       } else if (!entry.explicitlyAdded) {
  
positive.code:   /**
     * Create an analysis cache based on the given source [factory].
     */
    cache.AnalysisCache createCacheFromSourceFactory(SourceFactory factory) {
      if (factory == null) {
        return new cache.AnalysisCache(<cache.CachePartition>[_privatePartition]);
      }
      DartSdk sdk = factory.dartSdk;
      if (sdk == null) {
        return new cache.AnalysisCache(<cache.CachePartition>[_privatePartition]);
      }
      return new cache.AnalysisCache(<cache.CachePartition>[
        AnalysisEngine.instance.partitionManager_new.forSdk(sdk),
        _privatePartition
      ]);
  
negative.code:     // with two SdkCachePartition instances.
      InternalAnalysisContext sdkContext = sdk.context;
      // Check cache for an existing partition.
      SdkCachePartition partition = _sdkPartitions[sdk];
      if (partition == null) {
        partition = new SdkCachePartition(sdkContext);
        _sdkPartitions[sdk] = partition;
      }
      return partition;
  