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

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

Index: third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp
diff --git a/third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp b/third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp
index c5babd1c3c174b5756a853bae2016f5162dbff1b..582ee49e19980541a997a80133dccbb3f8502774 100644
--- a/third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp
+++ b/third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp
@@ -349,7 +349,7 @@ class TokenPreloadScanner::StartTagScanner {
     } 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());