Remove the Document.charset setter (making it readonly)

Source/core/loader/DocumentWriter.h

 /*
  * Copyright (C) 2010. Adam Barth. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 40 matching lines @@
     void end();
 
     void addData(const char* bytes, size_t length);
 
     const AtomicString& mimeType() const { return m_decoderBuilder.mimeType(); }
     const AtomicString& encoding() const { return m_decoderBuilder.encoding(); }
 
     // Exposed for DocumentLoader::replaceDocumentWhileExecutingJavaScriptURL.
     void appendReplacingData(const String&);
 
-    void setUserChosenEncoding(const String& charset);
-
     void setDocumentWasLoadedAsPartOfNavigation();
 
 private:
     DocumentWriter(Document*, ParserSynchronizationPolicy, const AtomicString& mimeType, const AtomicString& encoding);
 
     RawPtrWillBeMember<Document> m_document;
     TextResourceDecoderBuilder m_decoderBuilder;
 
     RefPtrWillBeMember<DocumentParser> m_parser;
 };
 
 } // namespace blink
 
 #endif // DocumentWriter_h