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

Source/core/html/HTMLDocument.h

Index: Source/core/html/HTMLDocument.h
diff --git a/Source/core/html/HTMLDocument.h b/Source/core/html/HTMLDocument.h
index 4eb35621397c7f47b1b6ab012152ec5e91e63436..472791dbc008618becc5105b70cd5bb5851b1127 100644
--- a/Source/core/html/HTMLDocument.h
+++ b/Source/core/html/HTMLDocument.h
@@ -74,6 +74,12 @@ public:
 
     virtual PassRefPtrWillBeRawPtr<Document> cloneDocumentWithoutChildren() OVERRIDE FINAL;
 
+    virtual void trace(Visitor* visitor) OVERRIDE
+    {
+        Document::trace(visitor);
+        ResourceClient::trace(visitor);
+    }
+
 protected:
     HTMLDocument(const DocumentInit&, DocumentClassFlags extendedDocumentClasses = DefaultDocumentClass);