Mark proxy map as unstable during fixing freezing, sealing or preventing extensions).

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 1ac1b5e8c4525f0a598eacd536865d6fed4276b9..dbeb0d841e6c72f332dda83bf4390dc364b48207 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6341,6 +6341,10 @@ class Map: public HeapObject {
                                               PropertyAttributes attrs_to_add,
                                               Handle<Symbol> transition_marker,
                                               const char* reason);
+
+  static Handle<Map> FixProxy(Handle<Map> map, InstanceType type, int size);
+
+
   // Maximal number of fast properties. Used to restrict the number of map
   // transitions to avoid an explosion in the number of maps for objects used as
   // dictionaries.