http: explain the unused argument in IncomingMessage._read

Author: Ayase-252

lib/_http_incoming.js

@@ -151,7 +151,10 @@ IncomingMessage.prototype.setTimeout = function setTimeout(msecs, callback) {
   return this;
 };
 
-
+// Argument n cannot be factored out due to the overhead of
+// argument adaptor frame creation inside V8 in case that number of actual
+// arguments is different from expected arguments.
+// Ref: https://bugs.chromium.org/p/v8/issues/detail?id=10201
 IncomingMessage.prototype._read = function _read(n) {
   if (!this._consuming) {
     this._readableState.readingMore = false;