anchor.diff:    final ScopeDigestTTL _ttl;
     final VmTurnZone _zone;
   
  +  // For Scope.watch().
  +  final Map<String, AST> astCache = new HashMap<String, AST>();
  +
     _FunctionChain _runAsyncHead, _runAsyncTail;
     _FunctionChain _domWriteHead, _domWriteTail;
     _FunctionChain _domReadHead, _domReadTail;
  
positive.code:     for(num i = 0; i <= _ttl.ttl; i++) {
        _digestTags.add(new UserTag('NgDigest${i}'));
      }
    }
  
    RootScope get rootScope => this;
  
negative.code: 
    RootScope(Object context, Parser parser, ASTParser astParser,
              FieldGetterFactory fieldGetterFactory, FormatterMap formatters, this._exceptionHandler,
              ScopeDigestTTL ttl, this._zone, ScopeStats _scopeStats, CacheRegister cacheRegister)
        : _scopeStats = _scopeStats,
          _ttl = ttl,
          _parser = parser,
  