Support as=<UPPERCASE VALUE> for link preloads in preload scanner

third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009 Torch Mobile, Inc. http://www.torchmobile.com/
  * 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 331 matching lines @@
       m_linkIsPreconnect = rel.isPreconnect();
       m_linkIsPreload = rel.isLinkPreload();
       m_linkIsImport = rel.isImport();
     } else if (match(attributeName, mediaAttr)) {
       m_matched &= mediaAttributeMatches(*m_mediaValues, attributeValue);
     } else if (match(attributeName, crossoriginAttr)) {
       setCrossOrigin(attributeValue);
     } else if (match(attributeName, nonceAttr)) {
       setNonce(attributeValue);
     } else if (match(attributeName, asAttr)) {
-      m_asAttributeValue = attributeValue;
+      m_asAttributeValue = attributeValue.lower();
     } else if (match(attributeName, typeAttr)) {
       m_matched &= MIMETypeRegistry::isSupportedStyleSheetMIMEType(
           ContentType(attributeValue).type());
     } else if (!m_referrerPolicySet &&
                match(attributeName, referrerpolicyAttr) &&
                !attributeValue.isNull()) {
       m_referrerPolicySet = true;
       SecurityPolicy::referrerPolicyFromString(attributeValue,
                                                &m_referrerPolicy);
     }
@@ skipping 540 matching lines @@
   defaultViewportMinWidth = document->viewportDefaultMinWidth();
   viewportMetaZeroValuesQuirk =
       document->settings() &&
       document->settings()->viewportMetaZeroValuesQuirk();
   viewportMetaEnabled =
       document->settings() && document->settings()->viewportMetaEnabled();
   referrerPolicy = document->getReferrerPolicy();
 }
 
 }  // namespace blink