Oilpan: fix g++ (4.8) building after r180659.

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 144 matching lines @@
     NumberOfFinalizedHeaps = GeneralHeapNonFinalized,
     NumberOfNonFinalizedHeaps = NumberOfHeaps - NumberOfFinalizedHeaps,
     NonFinalizedHeapOffset = FirstNonFinalizedHeap
 };
 
 // Base implementation for HeapIndexTrait found below.
 template<int heapIndex>
 struct HeapIndexTraitBase {
     typedef ThreadHeap<FinalizedHeapObjectHeader> HeapType;
     static const int finalizedIndex = heapIndex;
-    static const int nonFinalizedIndex = heapIndex + NonFinalizedHeapOffset;
+    static const int nonFinalizedIndex = heapIndex + static_cast<int>(NonFinalizedHeapOffset);
     static int index(bool isFinalized)
     {
         return isFinalized ? finalizedIndex : nonFinalizedIndex;
     }
 };
 
 // HeapIndexTrait defines properties for each heap in the TypesHeaps enum.
 template<int index>
 struct HeapIndexTrait;
 
@@ skipping 631 matching lines @@
     // HeapPage header. We use some of the bits to determine
     // whether the page is part of a terminting thread or
     // if the page is traced after being terminated (orphaned).
     uintptr_t m_terminating : 1;
     uintptr_t m_tracedAfterOrphaned : 1;
 };
 
 }
 
 #endif // ThreadState_h