Try harder to make sure that blink::FrameTree::m_uniqueName is truly unique.

third_party/WebKit/Source/core/page/FrameTree.h

 /*
  * Copyright (C) 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 64 matching lines @@
         const AtomicString& name,
         const AtomicString& fallbackName = nullAtom) const;
 
 private:
     Frame* deepLastChild() const;
     AtomicString calculateUniqueNameForChildFrame(
         bool existingChildFrame,
         const AtomicString& name,
         const AtomicString& fallbackName = nullAtom) const;
     bool uniqueNameExists(const AtomicString& name) const;
+    AtomicString ensureUniquenessOfUniqueName(const AtomicString& potentiallyUniqueName) const;
+    void setUniqueName(const AtomicString&);
 
     Member<Frame> m_thisFrame;
 
     AtomicString m_name; // The actual frame name (may be empty).
     AtomicString m_uniqueName;
 
     mutable unsigned m_scopedChildCount;
 };
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 void showFrameTree(const blink::Frame*);
 #endif
 
 #endif // FrameTree_h