Oilpan: Ensure that classes with virtual trace methods always have vtables for their left-most base…

Source/core/fetch/MemoryCache.h

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller <mueller@kde.org>
     Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later version.
 
@@ skipping 113 matching lines @@
 
 WTF_ALLOW_MOVE_INIT_AND_COMPARE_WITH_MEM_FUNCTIONS(blink::MemoryCacheLRUList);
 
 namespace blink {
 
 class MemoryCache FINAL : public NoBaseWillBeGarbageCollectedFinalized<MemoryCache>, public WebThread::TaskObserver {
     WTF_MAKE_NONCOPYABLE(MemoryCache); WTF_MAKE_FAST_ALLOCATED_WILL_BE_REMOVED;
 public:
     static PassOwnPtrWillBeRawPtr<MemoryCache> create();
     ~MemoryCache();
-    void trace(Visitor*);
+    virtual void trace(Visitor*);
 
     struct TypeStatistic {
         int count;
         int size;
         int liveSize;
         int decodedSize;
         int encodedSize;
         int encodedSizeDuplicatedInDataURLs;
         int purgeableSize;
         int purgedSize;
@@ skipping 152 matching lines @@
 // Returns the global cache.
 MemoryCache* memoryCache();
 
 // Sets the global cache, used to swap in a test instance. Returns the old
 // MemoryCache object.
 PassOwnPtrWillBeRawPtr<MemoryCache> replaceMemoryCacheForTesting(PassOwnPtrWillBeRawPtr<MemoryCache>);
 
 }
 
 #endif