anchor.diff:  
     static ZoneDelegate? _rootDelegate;
   
  -  ZoneDelegate get _delegate => _rootDelegate ??= new _ZoneDelegate(this);
  +  ZoneDelegate get _delegate => _rootDelegate ??= _ZoneDelegate(this);
     // It's a lie, but the root zone never uses the parent delegate.
     ZoneDelegate get _parentDelegate => _delegate;
   
  
positive.code: /// The function must only access zone-related functionality through
  /// [self], [parent] or [zone].
  /// It should not depend on the current zone ([Zone.current]).
  typedef Timer CreatePeriodicTimerHandler(Zone self, ZoneDelegate parent,
      Zone zone, Duration period, void f(Timer timer));
  
  /// The type of a custom [Zone.print] implementation function.
  ///
  
negative.code: /// The function must only access zone-related functionality through
  /// [self], [parent] or [zone].
  /// It should not depend on the current zone ([Zone.current]).
  typedef ErrorCallbackHandler = AsyncError? Function(Zone self,
      ZoneDelegate parent, Zone zone, Object error, StackTrace? stackTrace);
  
  /// The type of a custom [Zone.scheduleMicrotask] implementation function.
  ///
  