timers: attach listOnTimeout function to TimerWrap

Make the listOnTimeout function inline by attaching it to the TimeWrap
prototype.
It improves insertion and cancellation time of unpooled timers by 18%
and 28% respectively.

PR-URL: nodejs#18388
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

lib/timers.js

@@ -218,11 +218,11 @@ function TimersList(msecs, unrefed) {
   if (unrefed === true)
     timer.unref();
   timer.start(msecs);
-
-  timer[kOnTimeout] = listOnTimeout;
 }
 
-function listOnTimeout() {
+// adds listOnTimeout to the C++ object prototype, as
+// V8 would not inline it otherwise.
+TimerWrap.prototype[kOnTimeout] = function listOnTimeout() {
   var list = this._list;
   var msecs = list.msecs;
 
@@ -291,7 +291,7 @@ function listOnTimeout() {
     return;
 
   this.close();
-}
+};
 
 
 // An optimization so that the try/finally only de-optimizes (since at least v8