Add tests for trace wrappers

third_party/WebKit/Source/platform/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 989 matching lines @@
 
 void ThreadState::makeConsistentForMutator()
 {
     ASSERT(isInGC());
     for (int i = 0; i < BlinkGC::NumberOfArenas; ++i)
         m_arenas[i]->makeConsistentForMutator();
 }
 
 void ThreadState::preGC()
 {
-    if (RuntimeEnabledFeatures::traceWrappablesEnabled() && m_performCleanup)
+    if (RuntimeEnabledFeatures::traceWrappablesEnabled() && m_isolate && m_performCleanup)
         m_performCleanup(m_isolate);
 
     ASSERT(!isInGC());
     setGCState(GCRunning);
     makeConsistentForGC();
     flushHeapDoesNotContainCacheIfNeeded();
     clearArenaAges();
 
     // It is possible, albeit rare, for a thread to be kept
     // at a safepoint across multiple GCs, as resuming all attached
@@ skipping 726 matching lines @@
     for (int i = 0; i < 5; ++i) {
         collectGarbage(BlinkGC::NoHeapPointersOnStack, BlinkGC::GCWithSweep, BlinkGC::ForcedGC);
         size_t liveObjects = heap().heapStats().markedObjectSize();
         if (liveObjects == previousLiveObjects)
             break;
         previousLiveObjects = liveObjects;
     }
 }
 
 } // namespace blink