Add <link rel=preconnect> crossorigin attribute (take 2)

Source/core/html/CrossOriginAttribute.cpp

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "core/html/CrossOriginAttribute.h"
+
+namespace blink {
+
+CrossOriginAttributeValue crossOriginAttributeValue(const String& value)
+{
+    if (value.isNull())
+        return CrossOriginAttributeNotSet;
+    if (equalIgnoringCase(value, "use-credentials"))
+        return CrossOriginAttributeUseCredentials;
+    return CrossOriginAttributeAnonymous;
+}
+
+} // namespace blink
+