Fix test crashes by doing an additional GC on cleanup.

Source/heap/ThreadState.cpp

 /*
  * Copyright (C) 2013 Google Inc. 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
@@ skipping 280 matching lines @@
     // From here on ignore all conservatively discovered
     // pointers into the heap owned by this thread.
     m_isCleaningUp = true;
 
     for (size_t i = 0; i < m_cleanupTasks.size(); i++)
         m_cleanupTasks[i]->preCleanup();
 
     // After this GC we expect heap to be empty because
     // preCleanup tasks should have cleared all persistent
     // handles that were externally owned.
+    // FIXME: oilpan: we should perform a single GC and everything
+    // should die. Unfortunately it is not the case for all objects
+    // because the hierarchy was not completely moved to the heap and
+    // some heap allocated objects own objects that contain persistents
+    // pointing to other heap allocated objects.
+    Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
 
     // Verify that all heaps are empty now.
     for (int i = 0; i < NumberOfHeaps; i++)
         m_heaps[i]->assertEmpty();
 
     for (size_t i = 0; i < m_cleanupTasks.size(); i++)
         m_cleanupTasks[i]->postCleanup();
 
     m_cleanupTasks.clear();
@@ skipping 385 matching lines @@
     state->safePoint(HeapPointersOnStack);
 }
 
 ThreadState::AttachedThreadStateSet& ThreadState::attachedThreads()
 {
     DEFINE_STATIC_LOCAL(AttachedThreadStateSet, threads, ());
     return threads;
 }
 
 }