Implement UI support for manifest lists

image/docker/schema2/list.py

@@ -228,6 +228,10 @@ class DockerSchema2ManifestList(ManifestInterface):
   def local_blob_digests(self):
     return self.blob_digests
 
+  @property
+  def layers_compressed_size(self):
+    return None
+
   @lru_cache(maxsize=1)
   def manifests(self, lookup_manifest_fn):
     """ Returns the manifests in the list. The `lookup_manifest_fn` is a function