anchor.diff:        incrementalResolutionValidation_lastUnitSource = null;
         incrementalResolutionValidation_lastLibrarySource = null;
         incrementalResolutionValidation_lastUnit = null;
  -      // prepare the entry
  +      // prepare the source entry
         CacheEntry sourceEntry = _cache.get(unitSource);
         if (sourceEntry == null) {
           return false;
  
positive.code:         return false;
        }
        Source librarySource = librarySources[0];
        CacheEntry unitEntry =
            _cache.get(new LibrarySpecificUnit(librarySource, unitSource));
        if (unitEntry == null) {
          return false;
        }
        // prepare the library element
        LibraryElement libraryElement = getLibraryElement(librarySource);
        if (libraryElement == null) {
          return false;
        }
        // prepare the existing unit
        CompilationUnit oldUnit =
            getResolvedCompilationUnit2(unitSource, librarySource);
        if (oldUnit == null) {
          return false;
        }
  
negative.code:     List<ChangeNotice> notices = new List.from(_pendingNotices.values);
      _pendingNotices.clear();
      return notices;
    }
  
    /**
     * Return a [CompilationUnit] for the given library and unit sources, which
     * can be incrementally resolved.
     */
    CompilationUnit _getIncrementallyResolvableUnit(
        Source librarySource, Source unitSource) {
      LibrarySpecificUnit target =
          new LibrarySpecificUnit(librarySource, unitSource);
      for (ResultDescriptor result in [
        RESOLVED_UNIT,
        RESOLVED_UNIT11,
        RESOLVED_UNIT10,
        RESOLVED_UNIT9,
        RESOLVED_UNIT8,
        RESOLVED_UNIT7,
        RESOLVED_UNIT6
      ]) {
        CompilationUnit unit = getResult(target, result);
        if (unit != null) {
          return unit;
        }
      }
      return null;
    }
  
    /**
  