anchor.diff:  bool _isInAccessibilityMode(BuildContext context) {
     final MediaQueryData data = MediaQuery.of(context, nullOk: true);
     return data != null && data.textScaleFactor > _kMaxRegularTextScaleFactor;
  -}
  -
  -/// An iOS-style dialog.
  -///
  -/// This dialog widget does not have any opinion about the contents of the
  -/// dialog. Rather than using this widget directly, consider using
  -/// [CupertinoAlertDialog], which implement a specific kind of dialog.
  -///
  -/// Push with `Navigator.of(..., rootNavigator: true)` when using with
  -/// [CupertinoTabScaffold] to ensure that the dialog appears above the tabs.
  -///
  -/// See also:
  -///
  -///  * [CupertinoAlertDialog], which is a dialog with title, contents, and
  -///    actions.
  -///  * <https://developer.apple.com/ios/human-interface-guidelines/views/alerts/>
  -class CupertinoDialog extends StatelessWidget {
  -  /// Creates an iOS-style dialog.
  -  const CupertinoDialog({
  -    Key key,
  -    this.child,
  -  }) : super(key: key);
  -
  -  /// The widget below this widget in the tree.
  -  final Widget child;
  -
  -  @override
  -  Widget build(BuildContext context) {
  -    return new Center(
  -      child: new ClipRRect(
  -        borderRadius: BorderRadius.circular(_kDialogCornerRadius),
  -        child: new BackdropFilter(
  -          filter: new ImageFilter.blur(sigmaX: _kBlurAmount, sigmaY: _kBlurAmount),
  -          child: new Container(
  -            width: _kCupertinoDialogWidth,
  -            decoration: _kCupertinoDialogBlurOverlayDecoration,
  -            child: new Container(
  -              color: _kDialogColor,
  -              child: child,
  -            ),
  -          ),
  -        ),
  -      ),
  -    );
  -  }
   }
   
   /// An iOS-style alert dialog.
  
positive.code:               width: isInAccessibilityMode
                    ? _kAccessibilityCupertinoDialogWidth
                    : _kCupertinoDialogWidth,
                // The following clip is critical. The BackdropFilter needs to have
                // rounded corners, but Skia cannot internally create a blurred rounded
                // rect. Therefore, we have no choice but to clip, ourselves.
                // TODO(mattcarroll): Skia bug filed: https://bugs.chromium.org/p/skia/issues/detail?id=8238
                child: ClipRRect(
                  borderRadius: BorderRadius.circular(_kDialogCornerRadius),
                  child: new BackdropFilter(
                    filter: new ImageFilter.blur(sigmaX: _kBlurAmount, sigmaY: _kBlurAmount),
                    child: new Container(
                      decoration: _kCupertinoDialogBlurOverlayDecoration,
                      child: new _CupertinoDialogRenderWidget(
                        contentSection: _buildContent(),
                        actionsSection: _buildActions(),
                      ),
                    ),
                  ),
                ),
              ),
            );
          },
        ),
      );
    }
  
negative.code: ///
  /// See also:
  ///
  ///  * [CupertinoPopupSurface], which is a generic iOS-style popup surface that
  ///    holds arbitrary content to create custom popups.
  ///  * [CupertinoDialogAction], which is an iOS-style dialog button.
  ///  * <https://developer.apple.com/ios/human-interface-guidelines/views/alerts/>
  class CupertinoAlertDialog extends StatelessWidget {
  