anchor.diff:     * Virtual [ContextInfo] which acts as the ancestor of all other
      * [ContextInfo]s.
      */
  -  final ContextInfo _ancestorInfo = new ContextInfo._ancestor();
  +  final ContextInfo _rootInfo = new ContextInfo._root();
   
     ContextManagerImpl(this.resourceProvider, this.packageResolverProvider,
         this._packageMapProvider, this._instrumentationService) {
  
positive.code:         return folder.isOrContains(includedFolder.path);
        });
        if (!wasIncluded) {
          _createContexts(_ancestorInfo, includedFolder, false);
        }
      }
      // remove newly excluded sources
  
negative.code:           String directoryPath = pathContext.dirname(path);
  
            // Check to see if we need to create a new context.
            if (info.isTopLevel) {
  
              // Only create a new context if this is not the same directory
              // described by our info object.
  