Implement UI support for manifest lists

image/docker/interfaces.py

@@ -46,6 +46,12 @@ class ManifestInterface(object):
     """
     pass
 
+  @abstractproperty
+  def layers_compressed_size(self):
+    """ Returns the total compressed size of all the layers in this manifest. Returns None if this
+        cannot be computed locally.
+    """
+
   @abstractproperty
   def blob_digests(self):
     """ Returns an iterator over all the blob digests referenced by this manifest,