Add Blink APIs for frame tree mirroring.

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 a8bbe75f0965eeeae6bf8301273f91145de9c8e0..87ab2c6232c715c9d95b4c98186732342e03b583 100644
--- a/Source/core/html/HTMLFrameOwnerElement.h
+++ b/Source/core/html/HTMLFrameOwnerElement.h
@@ -39,6 +39,8 @@ public:
 
     // FrameOwner overrides:
     virtual bool isLocal() const { return true; }
+    virtual void setContentFrame(Frame&) OVERRIDE;
+    virtual void clearContentFrame() OVERRIDE;

[abarth-chromium, 2014/06/13 18:06:46]

This can still be private.  That will force callers to use FrameOwner's
interface.

[dcheng, 2014/06/13 23:56:12]

Done.

     virtual SandboxFlags sandboxFlags() const OVERRIDE { return m_sandboxFlags; }
     virtual void dispatchLoad() OVERRIDE;
 
@@ -46,9 +48,6 @@ public:
     DOMWindow* contentWindow() const;
     Document* contentDocument() const;
 
-    void setContentFrame(Frame&);
-    void clearContentFrame();
-
     void disconnectContentFrame();
 
     // Most subclasses use RenderPart (either RenderEmbeddedObject or RenderIFrame)