The deferred handes list belongs to the Isolate and not to the

src/heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5680 matching lines @@
   if (isolate_->deoptimizer_data() != NULL) {
     isolate_->deoptimizer_data()->Iterate(v);
   }
 #endif
   v->Synchronize(VisitorSynchronization::kDebug);
   isolate_->compilation_cache()->Iterate(v);
   v->Synchronize(VisitorSynchronization::kCompilationCache);
 
   // Iterate over local handles in handle scopes.
   isolate_->handle_scope_implementer()->Iterate(v);
+  isolate_->IterateDeferredHandles(v);
   v->Synchronize(VisitorSynchronization::kHandleScope);
 
   // Iterate over the builtin code objects and code stubs in the
   // heap. Note that it is not necessary to iterate over code objects
   // on scavenge collections.
   if (mode != VISIT_ALL_IN_SCAVENGE) {
     isolate_->builtins()->IterateBuiltins(v);
   }
   v->Synchronize(VisitorSynchronization::kBuiltins);
 
@@ skipping 1511 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   CODE_KIND_LIST(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   memcpy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   memcpy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 
 } }  // namespace v8::internal