Disallow local/remote checks on subclasses of Frame, FrameOwner and DOMWindow.

third_party/WebKit/Source/core/frame/RemoteDOMWindow.h

Index: third_party/WebKit/Source/core/frame/RemoteDOMWindow.h
diff --git a/third_party/WebKit/Source/core/frame/RemoteDOMWindow.h b/third_party/WebKit/Source/core/frame/RemoteDOMWindow.h
index d65e44f30ec3c4c0878d9f3eb3508f62c98ce2d3..fe40e769304bbbb6fde6f28522aec282e4c3ff0b 100644
--- a/third_party/WebKit/Source/core/frame/RemoteDOMWindow.h
+++ b/third_party/WebKit/Source/core/frame/RemoteDOMWindow.h
@@ -22,7 +22,6 @@ public:
 
     // DOMWindow overrides:
     DECLARE_VIRTUAL_TRACE();
-    bool isRemoteDOMWindow() const override { return true; }
     RemoteFrame* frame() const override;
     Screen* screen() const override;
     History* history() const override;
@@ -88,6 +87,11 @@ protected:
 private:
     explicit RemoteDOMWindow(RemoteFrame&);
 
+    // Intentionally private to prevent redundant checks when the type is
+    // already RemoteDOMWindow.
+    bool isLocalDOMWindow() const override { return false; }
+    bool isRemoteDOMWindow() const override { return true; }
+
     Member<RemoteFrame> m_frame;
 };