Show deprecation warnings for header values in XHR according to RFC 7230

Source/core/xmlhttprequest/XMLHttpRequest.cpp

 /*
  *  Copyright (C) 2004, 2006, 2008 Apple Inc. All rights reserved.
  *  Copyright (C) 2005-2007 Alexey Proskuryakov <ap@webkit.org>
  *  Copyright (C) 2007, 2008 Julien Chaffraix <jchaffraix@webkit.org>
  *  Copyright (C) 2008, 2011 Google Inc. All rights reserved.
  *  Copyright (C) 2012 Intel Corporation
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
@@ skipping 1160 matching lines @@
     if (m_state != OPENED || m_loader) {
         exceptionState.throwDOMException(InvalidStateError, "The object's state must be OPENED.");
         return;
     }
 
     if (!isValidHTTPToken(name)) {
         exceptionState.throwDOMException(SyntaxError, "'" + name + "' is not a valid HTTP header field name.");
         return;
     }
 
+    // Show deprecation warnings and count occurrences of such deprecated header values
+    if (isValidHTTPHeaderValueForFetch(value))

[hiroshige, 2015/08/27 11:38:08]

How about replacing this with "if (!isValidHTTPHeaderValueForFetch(value))" and
placing this after the "if (!isValidHTTPHeaderValue(value)) {...}" block?

i.e. we want to warn header values that pass
isValidHTTPHeaderValue() but don't pass
isValidHTTPHeaderValueForFetch().

[shiva.jm, 2015/09/01 08:26:51]

Done.

+        UseCounter::countDeprecation(executionContext(), UseCounter::FetchHeaderValue);
+
     if (!isValidHTTPHeaderValue(value)) {
         exceptionState.throwDOMException(SyntaxError, "'" + value + "' is not a valid HTTP header field value.");
         return;
     }
 
     // No script (privileged or not) can set unsafe headers.
     if (FetchUtils::isForbiddenHeaderName(name)) {
         logConsoleError(executionContext(), "Refused to set unsafe header \"" + name + "\"");
         return;
     }
@@ skipping 502 matching lines @@
     visitor->trace(m_responseDocumentParser);
     visitor->trace(m_progressEventThrottle);
     visitor->trace(m_upload);
     visitor->trace(m_blobLoader);
     XMLHttpRequestEventTarget::trace(visitor);
     DocumentParserClient::trace(visitor);
     ActiveDOMObject::trace(visitor);
 }
 
 } // namespace blink