Add placeholder to DecorationImage when image is a network image. #187906

Container(
    height: 200,
    decoration: BoxDecoration(
      border: Border.all(color: Colors.blue),
      image: DecorationImage(
        image: CachedNetworkImageProvider(
          ‘https://seopic.699pic.com/photo/50053/2696.jpg_wh1200.jpg',
        ),
        placeholder: AssetImage(Assets.assetsImagesFlutter),// This !!!
        fit: BoxFit.fill,
      ),
    ),
  ),

@override
 void paint(
   Canvas canvas,
   Rect rect,
   Path? clipPath,
   ImageConfiguration configuration, {
   double blend = 1.0,
   BlendMode blendMode = BlendMode.srcOver,
 }) {
...
   if (_image != null) {
     _placeholderStream?.removeListener(_placeholderListener);
     _placeholderStream = null;
     _placeholderImage?.dispose();
     _placeholderImage = null;
   } else if (_details.placeholder != null) {
     final ImageStream placeholderStream = _details.placeholder!.resolve(configuration);
     if (placeholderStream.key != _placeholderStream?.key) {
       _placeholderStream?.removeListener(_placeholderListener);
       _placeholderStream = placeholderStream;
       _placeholderStream?.addListener(_placeholderListener);
     }
   }

   final ImageStream newImageStream = _details.image.resolve(configuration);
   if (newImageStream.key != _imageStream?.key) {
     _imageStream?.removeListener(_imageListener);
     _imageStream = newImageStream;
     _imageStream!.addListener(_imageListener);
   }
   ImageInfo? imageInfo = _image ?? _placeholderImage;
   if (imageInfo == null) {
     return;
   }

   if (clipPath != null) {
     canvas.save();
     canvas.clipPath(clipPath);
   }

   paintImage(
     canvas: canvas,
     rect: rect,
     image: imageInfo.image,
     debugImageLabel: imageInfo.debugLabel,
...
}

 void _handlePlaceholder(ImageInfo value, bool synchronousCall) {
   if (_image != null) {
     value.dispose();
     return;
   }
   if (_placeholderImage == value) {
     return;
   }
   _placeholderImage?.dispose();
   _placeholderImage = value;
   if (!synchronousCall) {
     _onChanged();
   }
 }