Update interfaces/shape-detection-api.idl (#13352)

Source: https://github.com/tidoust/reffy-reports/blob/f128525/whatwg/idl/shape-detection-api.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/436975697
diff --git a/interfaces/shape-detection-api.idl b/interfaces/shape-detection-api.idl
index dbdf022..66c5889 100644
--- a/interfaces/shape-detection-api.idl
+++ b/interfaces/shape-detection-api.idl
@@ -14,6 +14,7 @@
   boolean fastMode;
 };
 
+[Serializable]
 interface DetectedFace {
   [SameObject] readonly attribute DOMRectReadOnly boundingBox;
   [SameObject] readonly attribute FrozenArray<Landmark>? landmarks;
@@ -42,6 +43,7 @@
   sequence<BarcodeFormat> formats;
 };
 
+[Serializable]
 interface DetectedBarcode {
   [SameObject] readonly attribute DOMRectReadOnly boundingBox;
   [SameObject] readonly attribute DOMString rawValue;