Add Blink APIs for frame tree mirroring.

Source/core/frame/Frame.cpp

Index: Source/core/frame/Frame.cpp
diff --git a/Source/core/frame/Frame.cpp b/Source/core/frame/Frame.cpp
index db3f719f5951b14d8bae71fdb31142411de8e2df..c741b7b5192af47dbb9fb50a50ca20ddd860895a 100644
--- a/Source/core/frame/Frame.cpp
+++ b/Source/core/frame/Frame.cpp
@@ -71,8 +71,7 @@ Frame::Frame(FrameClient* client, FrameHost* host, FrameOwner* owner)
 
     if (m_owner) {
         page()->incrementSubframeCount();
-        if (m_owner->isLocal())
-            toHTMLFrameOwnerElement(m_owner)->setContentFrame(*this);
+        m_owner->setContentFrame(*this);
     }
 }
 
@@ -185,8 +184,7 @@ bool Frame::isMainFrame() const
 void Frame::disconnectOwnerElement()
 {
     if (m_owner) {
-        if (m_owner->isLocal())
-            toHTMLFrameOwnerElement(m_owner)->clearContentFrame();
+        m_owner->clearContentFrame();
         if (page())
             page()->decrementSubframeCount();
     }