Preprocess structured stack trace on GC to get rid of code reference.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 06f93040925c85118914093b2769ac2fc7f5b3f6..2c8a6bc66d206f68e75f1a4f95fff5bb5daf6f11 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -186,7 +186,8 @@ namespace internal {
   V(FixedArray, detached_contexts, DetachedContexts)                           \
   V(ArrayList, retained_maps, RetainedMaps)                                    \
   V(WeakHashTable, weak_object_to_code_table, WeakObjectToCodeTable)           \
-  V(PropertyCell, array_protector, ArrayProtector)
+  V(PropertyCell, array_protector, ArrayProtector)                             \
+  V(Object, weak_stack_trace_list, WeakStackTraceList)
 
 // Entries in this list are limited to Smis and are not visited during GC.
 #define SMI_ROOT_LIST(V)                                                   \
@@ -1742,6 +1743,8 @@ class Heap {
   void GarbageCollectionPrologue();
   void GarbageCollectionEpilogue();
 
+  void PreprocessStackTraces();
+
   // Pretenuring decisions are made based on feedback collected during new
   // space evacuation. Note that between feedback collection and calling this
   // method object in old space must not move.