Report DOM partitionAlloc size to V8 GC.

Source/platform/Partitions.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 26 matching lines @@
 namespace WebCore {
 
 class PLATFORM_EXPORT Partitions {
 public:
     static void init();
     static void shutdown();
 
     ALWAYS_INLINE static PartitionRoot* getObjectModelPartition() { return m_objectModelAllocator.root(); }
     ALWAYS_INLINE static PartitionRoot* getRenderingPartition() { return m_renderingAllocator.root(); }
 
+    static size_t currentDOMMemoryUsage()
+    {
+        return m_objectModelAllocator.root()->totalSizeOfCommittedPages;
+    }
+
 private:
     static SizeSpecificPartitionAllocator<3072> m_objectModelAllocator;
     static SizeSpecificPartitionAllocator<1024> m_renderingAllocator;
 };
 
 } // namespace WebCore
 
 #endif // Partitions_h