Oilpan: fix build after r189304 (6a1bbc3).

Source/web/PopupMenuImpl.cpp

Index: Source/web/PopupMenuImpl.cpp
diff --git a/Source/web/PopupMenuImpl.cpp b/Source/web/PopupMenuImpl.cpp
index a03c13dcd202d9e281f3d8c6d69cc376ceda9811..40e7b84c254afe7744aaae3ba7690e520e323f45 100644
--- a/Source/web/PopupMenuImpl.cpp
+++ b/Source/web/PopupMenuImpl.cpp
@@ -33,10 +33,15 @@ public:
     // only worked with fonts loaded when opening the popup.
     virtual PassRefPtr<FontData> getFontData(const FontDescription&, const AtomicString&) override;
 
+    virtual void trace(Visitor*) override;
+
 private:
     PopupMenuCSSFontSelector(Document* document, CSSFontSelector* ownerFontSelector)
         : CSSFontSelector(document)
-        , m_ownerFontSelector(ownerFontSelector) { }
+        , m_ownerFontSelector(ownerFontSelector)
+    {
+    }
+
     RefPtrWillBeMember<CSSFontSelector> m_ownerFontSelector;
 };
 
@@ -45,6 +50,12 @@ PassRefPtr<FontData> PopupMenuCSSFontSelector::getFontData(const FontDescription
     return m_ownerFontSelector->getFontData(description, name);
 }
 
+void PopupMenuCSSFontSelector::trace(Visitor* visitor)
+{
+    visitor->trace(m_ownerFontSelector);
+    CSSFontSelector::trace(visitor);
+}
+
 PassRefPtrWillBeRawPtr<PopupMenuImpl> PopupMenuImpl::create(ChromeClientImpl* chromeClient, PopupMenuClient* client)
 {
     return adoptRefWillBeNoop(new PopupMenuImpl(chromeClient, client));