Move FormDataList::setEntry to DOMFormData.

Source/core/html/DOMFormData.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 62 matching lines @@
     bool has(const String& name);
     void set(const String& name, const String& value);
     void set(const String& name, Blob*, const String& filename = String());
 
     void makeOpaque() { m_opaque = true; }
     bool opaque() const { return m_opaque; }
 
 private:
     explicit DOMFormData(const WTF::TextEncoding&);
     explicit DOMFormData(HTMLFormElement*);
+    void setEntry(const Item&);
 
     IterationSource* startIteration(ScriptState*, ExceptionState&) override;
     bool m_opaque;
 };
 
 } // namespace blink
 
 #endif // DOMFormData_h