Use WeakCell to handle the script wrapper cache

src/serialize.cc

Index: src/serialize.cc
diff --git a/src/serialize.cc b/src/serialize.cc
index 70b69c23c0dc01beeda05d4bcb2532584df4b5a6..8657ea38502ac185d66741f7816ecf12299ab90e 100644
--- a/src/serialize.cc
+++ b/src/serialize.cc
@@ -2018,10 +2018,11 @@ void CodeSerializer::SerializeHeapObject(HeapObject* heap_object,
                                          HowToCode how_to_code,
                                          WhereToPoint where_to_point) {
   if (heap_object->IsScript()) {
-    // The wrapper cache uses a Foreign object to point to a global handle.
-    // However, the object visitor expects foreign objects to point to external
-    // references.  Clear the cache to avoid this issue.
-    Script::cast(heap_object)->ClearWrapperCache();
+    // The wrapper cache uses a WeakCell.  However it's not clear what
+    // the semantics of WeakCell are when serializing.  For now we just
+    // clear the cache.
+    HeapObject* clear = heap_object->GetHeap()->undefined_value();

[ulan, 2014/10/14 15:45:56]

Since we rebuild the WeakCell list on every GC, serialization should work
correctly.

+    Script::cast(heap_object)->set_wrapper(clear);

[ulan, 2014/10/14 15:45:56]

Should we also isolate->counters()->script_wrappers()->Decrement() ?

   }
 
   if (FLAG_trace_code_serializer) {