Implement referrerpolicy attr for iframes

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 87ad3856ec50b56c797c85a6dd4ef71339d38373..f0236a61cdf5a2dde0c7aeb34f669f7818437433 100644
--- a/Source/core/html/HTMLFrameOwnerElement.h
+++ b/Source/core/html/HTMLFrameOwnerElement.h
@@ -27,6 +27,7 @@
 #include "core/html/HTMLElement.h"
 #include "platform/heap/Handle.h"
 #include "platform/scroll/ScrollTypes.h"
+#include "platform/weborigin/SecurityPolicy.h"
 #include "wtf/HashCountedSet.h"
 
 namespace blink {
@@ -94,6 +95,8 @@ private:
     bool isKeyboardFocusable() const override;
     bool isFrameOwnerElement() const final { return true; }
 
+    virtual ReferrerPolicy referrerPolicyAttribute() { return ReferrerPolicyDefault; }
+
     RawPtrWillBeMember<Frame> m_contentFrame;
     RefPtrWillBeMember<Widget> m_widget;
     SandboxFlags m_sandboxFlags;