Move renderFallbackContent() into FrameOwner interface.

Source/core/html/HTMLFrameOwnerElement.h

Index: Source/core/html/HTMLFrameOwnerElement.h
diff --git a/Source/core/html/HTMLFrameOwnerElement.h b/Source/core/html/HTMLFrameOwnerElement.h
index 53f240a5ca99b9d4efb15dffdb64bc14d03f4e53..fd6440632857a0a42b562ccf39ee406c34ead493 100644
--- a/Source/core/html/HTMLFrameOwnerElement.h
+++ b/Source/core/html/HTMLFrameOwnerElement.h
@@ -63,9 +63,6 @@ public:
     virtual bool loadedNonEmptyDocument() const { return false; }
     virtual void didLoadNonEmptyDocument() { }
 
-    virtual void renderFallbackContent() { }
-
-    virtual bool isObjectElement() const { return false; }
     void setWidget(PassRefPtrWillBeRawPtr<Widget>);
     Widget* ownedWidget() const;
 
@@ -79,9 +76,10 @@ public:
     };
 
     // FrameOwner overrides:
-    virtual bool isLocal() const { return true; }
-    virtual void dispatchLoad() override;
-    virtual SandboxFlags sandboxFlags() const override { return m_sandboxFlags; }
+    bool isLocal() const override { return true; }
+    void dispatchLoad() override;
+    SandboxFlags sandboxFlags() const override { return m_sandboxFlags; }
+    void renderFallbackContent() override { }
 
     DECLARE_VIRTUAL_TRACE();