Oilpan: fix computation of ThreadState::m_collectionRate.

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 616 matching lines @@
     StackState m_stackState;
     intptr_t* m_startOfStack;
     intptr_t* m_endOfStack;
     void* m_safePointScopeMarker;
     Vector<Address> m_safePointStackCopy;
     bool m_atSafePoint;
     Vector<Interruptor*> m_interruptors;
     bool m_didV8GCAfterLastGC;
     bool m_sweepForbidden;
     size_t m_noAllocationCount;
-    size_t m_allocatedObjectSizeBeforeSweeping;
+    size_t m_allocatedObjectSizeBeforeGC;
     ThreadHeap* m_heaps[NumberOfHeaps];
 
     Vector<OwnPtr<CleanupTask>> m_cleanupTasks;
     bool m_isTerminating;
 
     bool m_shouldFlushHeapDoesNotContainCache;
     double m_collectionRate;
     GCState m_gcState;
 
     CallbackStack* m_weakCallbackStack;
@@ skipping 77 matching lines @@
         m_locked = false;
     }
 
     MutexBase& m_mutex;
     bool m_locked;
 };
 
 } // namespace blink
 
 #endif // ThreadState_h