Oilpan: fix build after r353261, part 2.

third_party/WebKit/Source/core/html/HTMLAnchorElement.h

Index: third_party/WebKit/Source/core/html/HTMLAnchorElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLAnchorElement.h b/third_party/WebKit/Source/core/html/HTMLAnchorElement.h
index d37e6092b26c01c3e709d7a3238744ff0f189f65..deeae3f7a170723bbc249da1d3af7842fcb169c2 100644
--- a/third_party/WebKit/Source/core/html/HTMLAnchorElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLAnchorElement.h
@@ -59,8 +59,8 @@ enum {
 
 class CORE_EXPORT HTMLAnchorElement : public HTMLElement, public DOMURLUtils, public DOMSettableTokenListObserver {
     DEFINE_WRAPPERTYPEINFO();
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(HTMLAnchorElement);
 public:
-    DECLARE_VIRTUAL_TRACE();
     static PassRefPtrWillBeRawPtr<HTMLAnchorElement> create(Document&);
 
     ~HTMLAnchorElement() override;
@@ -90,6 +90,8 @@ public:
 
     DOMSettableTokenList* ping();
 
+    DECLARE_VIRTUAL_TRACE();
+
 protected:
     HTMLAnchorElement(const QualifiedName&, Document&);