revert: store header keys lower case internally (#12837)

This reverts commit 49ec3d10ad90851f4d28274a3f0fe96c642204ac.

1 files changed, 4 insertions, 2 deletions

diff --git a/ext/fetch/23_request.js b/ext/fetch/23_request.js
index 845e47877..b13b8e687 100644
--- a/ext/fetch/23_request.js
+++ b/ext/fetch/23_request.js
@@ -173,8 +173,10 @@
       let charset = null;
       let essence = null;
       let mimeType = null;
-      const headerList = headerListFromHeaders(this[_headers]);
-      const values = getDecodeSplitHeader(headerList, "content-type");
+      const values = getDecodeSplitHeader(
+        headerListFromHeaders(this[_headers]),
+        "Content-Type",
+      );
       if (values === null) return null;
       for (const value of values) {
         const temporaryMimeType = mimesniff.parseMimeType(value);