Remove the Document.charset setter (making it readonly)

Source/core/html/parser/TextResourceDecoder.cpp

 /*
     Copyright (C) 1999 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
     Copyright (C) 2005, 2006, 2007 Alexey Proskuryakov (ap@nypop.com)
 
     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.
 
@@ skipping 312 matching lines @@
     } else if (bytesEqual(ptr, 0, 0, 0, '<', 0, 0, 0, '?')) {
         setEncoding(UTF32BigEndianEncoding(), AutoDetectedEncoding);
     }
 
     m_checkedForXMLCharset = true;
     return true;
 }
 
 void TextResourceDecoder::checkForMetaCharset(const char* data, size_t length)
 {
-    if (m_source == UserChosenEncoding || m_source == EncodingFromHTTPHeader || m_source == AutoDetectedEncoding) {
+    if (m_source == EncodingFromHTTPHeader || m_source == AutoDetectedEncoding) {
         m_checkedForMetaCharset = true;
         return;
     }
 
     if (!m_charsetParser)
         m_charsetParser = HTMLMetaCharsetParser::create();
 
     if (!m_charsetParser->checkForMetaCharset(data, length))
         return;
 
@@ skipping 89 matching lines @@
         m_codec = newTextCodec(m_encoding);
 
     String result = m_codec->decode(m_buffer.data(), m_buffer.size(), FetchEOF, m_contentType == XMLContent && !m_useLenientXMLDecoding, m_sawError);
     m_buffer.clear();
     m_codec.clear();
     m_checkedForBOM = false; // Skip BOM again when re-decoding.
     return result;
 }
 
 }