Use a plain FixedArray rather than a SeededNumberDictionary for ValueDeserializer::id_map_.

src/value-serializer.h

Index: src/value-serializer.h
diff --git a/src/value-serializer.h b/src/value-serializer.h
index 5114c23dc6005f71d7b52bf6b3a227fc180063b7..037c38eb320113fbc51b0aa729f68ed979fe2235 100644
--- a/src/value-serializer.h
+++ b/src/value-serializer.h
@@ -253,7 +253,7 @@ class ValueDeserializer {
   uint32_t next_id_ = 0;
 
   // Always global handles.
-  Handle<SeededNumberDictionary> id_map_;
+  Handle<FixedArray> id_map_;
   MaybeHandle<SeededNumberDictionary> array_buffer_transfer_map_;
 
   DISALLOW_COPY_AND_ASSIGN(ValueDeserializer);