VM: ProcessPendingWeakProperties must call VisitingOldObject(NULL) at the end.

runtime/vm/gc_marker.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/gc_marker.h"
 
 #include "vm/allocation.h"
 #include "vm/dart_api_state.h"
 #include "vm/isolate.h"
 #include "vm/log.h"
@@ skipping 183 matching lines @@
         // originating from this weak property.
         VisitingOldObject(cur_weak);
         cur_weak->VisitPointers(this);
       } else {
         // Requeue this weak property to be handled later.
         EnqueueWeakProperty(cur_weak);
       }
       // Advance to next weak property in the queue.
       cur_weak = reinterpret_cast<RawWeakProperty*>(next_weak);
     }
-
+    VisitingOldObject(NULL);
     return marked;
   }
 
   void DrainMarkingStack() {
     RawObject* raw_obj = work_list_.Pop();
     if ((raw_obj == NULL) && ProcessPendingWeakProperties()) {
       raw_obj = work_list_.Pop();
     }
 
     if (raw_obj == NULL) {
@@ skipping 536 matching lines @@
       // Phase 3: Finalize results from all markers (detach code, etc.).
       barrier.Exit();
     }
     ProcessWeakTables(page_space);
     ProcessObjectIdTable(isolate);
   }
   Epilogue(isolate, invoke_api_callbacks);
 }
 
 }  // namespace dart