Make objects embedded in optimized code weak.

src/serialize.cc

Index: src/serialize.cc
diff --git a/src/serialize.cc b/src/serialize.cc
index d05dd2612270c8e16f3f0c7d0354d94eaddbe49a..9edd1dcc4fff5386b795472881d4b4e69fff6a8c 100644
--- a/src/serialize.cc
+++ b/src/serialize.cc
@@ -835,6 +835,9 @@ void Deserializer::Deserialize(Isolate* isolate) {
         isolate_->heap()->undefined_value());
   }
 
+  isolate_->heap()->set_weak_object_to_code(
+      isolate_->heap()->undefined_value());
+
   // Update data pointers to the external strings containing natives sources.
   for (int i = 0; i < Natives::GetBuiltinsCount(); i++) {
     Object* source = isolate_->heap()->natives_source_cache()->get(i);