Allow Oilpan heap objects account for their external allocations.

Source/core/dom/Text.h

Index: Source/core/dom/Text.h
diff --git a/Source/core/dom/Text.h b/Source/core/dom/Text.h
index 1b4c0bf5594927bb2172308c8adb85cf227810b9..e0bf2d0378c355623fa65af4b7ee9c8f9f07f0ee 100644
--- a/Source/core/dom/Text.h
+++ b/Source/core/dom/Text.h
@@ -61,6 +61,10 @@ public:
     virtual bool canContainRangeEndPoint() const override final { return true; }
     virtual NodeType nodeType() const override;
 
+#if ENABLE(OILPAN)
+    virtual void trace(Visitor*) override;
+#endif
+
 protected:
     Text(TreeScope& treeScope, const String& data, ConstructionType type)
         : CharacterData(treeScope, data, type) { }