Manage WebGLRenderingContextBase's weak refs manually without Oilpan.

third_party/WebKit/Source/platform/heap/ThreadState.h

 /*
  * 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 762 matching lines @@
     intptr_t* m_endOfStack;
     void* m_safePointScopeMarker;
     Vector<Address> m_safePointStackCopy;
     bool m_atSafePoint;
     InterruptorVector m_interruptors;
     bool m_sweepForbidden;
     size_t m_noAllocationCount;
     size_t m_gcForbiddenCount;
     int m_persistentAllocated;
     int m_persistentFreed;
+    int m_pageNavigationCount;
     BaseHeap* m_heaps[NumberOfHeaps];
 
     int m_vectorBackingHeapIndex;
     size_t m_heapAges[NumberOfHeaps];
     size_t m_currentHeapAges;
 
     bool m_isTerminating;
     GarbageCollectedMixinConstructorMarker* m_gcMixinMarker;
 
     bool m_shouldFlushHeapDoesNotContainCache;
@@ skipping 38 matching lines @@
 };
 
 template<> class ThreadStateFor<AnyThread> {
 public:
     static ThreadState* state() { return ThreadState::current(); }
 };
 
 } // namespace blink
 
 #endif // ThreadState_h