Bug 1354989 - Avoid pivoting via UTF-16 when loading CSS in the Stylo mode. r=jdm,SimonSapin

MozReview-Commit-ID: Llt29dvB4Io

parser/html/nsHtml5TreeOpExecutor.cpp

@@ -984,7 +984,10 @@ nsHtml5TreeOpExecutor::PreloadStyle(const nsAString& aURL,
     referrerPolicy = styleReferrerPolicy;
   }
 
-  mDocument->PreloadStyle(uri, aCharset, aCrossOrigin, referrerPolicy,
+  mDocument->PreloadStyle(uri,
+                          Encoding::ForLabel(aCharset),
+                          aCrossOrigin,
+                          referrerPolicy,
                           aIntegrity);
 }