Report DOM partitionAlloc size to V8 GC.

Source/platform/Partitions.h

Index: Source/platform/Partitions.h
diff --git a/Source/platform/Partitions.h b/Source/platform/Partitions.h
index c589220f5fca4620c9c167a17dc47939030f9bab..2b6922eaba7e7b151e75d0e4ab9309e601f33d81 100644
--- a/Source/platform/Partitions.h
+++ b/Source/platform/Partitions.h
@@ -44,9 +44,23 @@ public:
     ALWAYS_INLINE static PartitionRoot* getObjectModelPartition() { return m_objectModelAllocator.root(); }
     ALWAYS_INLINE static PartitionRoot* getRenderingPartition() { return m_renderingAllocator.root(); }
 
+    static void addDOMMemoryUsage(size_t size)
+    {
+        m_domMemoryUsage += size;
+    }
+
+    static void subtractDOMMemoryUsage(size_t size)
+    {
+        m_domMemoryUsage -= size;
+    }
+
+    static size_t currentDOMMemoryUsage() { return m_domMemoryUsage; }
+
 private:
     static SizeSpecificPartitionAllocator<3072> m_objectModelAllocator;
     static SizeSpecificPartitionAllocator<1024> m_renderingAllocator;
+
+    static size_t m_domMemoryUsage;
 };
 
 } // namespace WebCore