Bug 1641245 - Make string comparators not virtual. r=froydnj,necko-reviewers,geckoview-reviewers,jgilbert,agi,valentin

There's no use case for stateful comparators, so they can be just plain
function pointers.

This is used in some hot places like CSS selector matching.

Differential Revision: https://phabricator.services.mozilla.com/D77084

image/ImageCacheKey.cpp

@@ -85,7 +85,7 @@ bool ImageCacheKey::operator==(const ImageCacheKey& aOther) const {
   // Don't share the image cache between two top-level documents of different
   // base domains.
   if (!mIsolationKey.Equals(aOther.mIsolationKey,
-                            nsCaseInsensitiveCStringComparator())) {
+                            nsCaseInsensitiveCStringComparator)) {
     return false;
   }
   // The origin attributes always have to match.