http: simplify isCookieField

Handrolling and checking char by char is no longer faster than just
using toLowerCase and strict comparison.

PR-URL: #20131
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yuta Hiroto <hello@hiroppy.me>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/_http_outgoing.js

@@ -58,24 +58,10 @@ var RE_CONN_VALUES = /(?:^|\W)close|upgrade(?:$|\W)/ig;
 var RE_TE_CHUNKED = common.chunkExpression;
 
 // isCookieField performs a case-insensitive comparison of a provided string
-// against the word "cookie." This method (at least as of V8 5.4) is faster than
-// the equivalent case-insensitive regexp, even if isCookieField does not get
-// inlined.
+// against the word "cookie." As of V8 6.6 this is faster than handrolling or
+// using a case-insensitive RegExp.
 function isCookieField(s) {
-  if (s.length !== 6) return false;
-  var ch = s.charCodeAt(0);
-  if (ch !== 99 && ch !== 67) return false;
-  ch = s.charCodeAt(1);
-  if (ch !== 111 && ch !== 79) return false;
-  ch = s.charCodeAt(2);
-  if (ch !== 111 && ch !== 79) return false;
-  ch = s.charCodeAt(3);
-  if (ch !== 107 && ch !== 75) return false;
-  ch = s.charCodeAt(4);
-  if (ch !== 105 && ch !== 73) return false;
-  ch = s.charCodeAt(5);
-  if (ch !== 101 && ch !== 69) return false;
-  return true;
+  return s.length === 6 && s.toLowerCase() === 'cookie';
 }
 
 function noopPendingOutput(amount) {}