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

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

Index: third_party/WebKit/Source/core/frame/LocalDOMWindow.h
diff --git a/third_party/WebKit/Source/core/frame/LocalDOMWindow.h b/third_party/WebKit/Source/core/frame/LocalDOMWindow.h
index a6e4d289c3a98002bdf09a4307cb81a757a0e85e..aec06af7756700d3d41d47d7f1ed8280ff0c738e 100644
--- a/third_party/WebKit/Source/core/frame/LocalDOMWindow.h
+++ b/third_party/WebKit/Source/core/frame/LocalDOMWindow.h
@@ -86,7 +86,6 @@ public:
     LocalDOMWindow* toLocalDOMWindow() override;
 
     // DOMWindow overrides:
-    bool isLocalDOMWindow() const override { return true; }
     LocalFrame* frame() const override;
     Screen* screen() const override;
     History* history() const override;
@@ -211,6 +210,11 @@ protected:
 private:
     class WindowFrameObserver;
 
+    // Intentionally private to prevent redundant checks when the type is
+    // already LocalDOMWindow.
+    bool isLocalDOMWindow() const override { return true; }
+    bool isRemoteDOMWindow() const override { return false; }
+
     explicit LocalDOMWindow(LocalFrame&);
     void dispose();