Fix memory leak caused by treating Code::next_code_link as strong in marker.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 1f97fc3859bddc841da80426bc0c4273f61db6bb..18b3315454e2bd7ae4c21807f00f84038b1a2ca5 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -4061,6 +4061,7 @@ MaybeObject* Heap::CreateCode(const CodeDesc& desc,
   code->set_is_crankshafted(crankshafted);
   code->set_deoptimization_data(empty_fixed_array(), SKIP_WRITE_BARRIER);
   code->set_raw_type_feedback_info(undefined_value());
+  code->set_next_code_link(undefined_value());
   code->set_handler_table(empty_fixed_array(), SKIP_WRITE_BARRIER);
   code->set_gc_metadata(Smi::FromInt(0));
   code->set_ic_age(global_ic_age_);