Implement UI support for manifest lists

image/docker/schema2/manifest.py

@@ -169,6 +169,10 @@ class DockerSchema2Manifest(ManifestInterface):
       self._layers = list(self._generate_layers())
     return self._layers
 
+  @property
+  def layers_compressed_size(self):
+    return sum(layer.compressed_size for layer in self.layers)
+
   @property
   def leaf_layer(self):
     return self.layers[-1]