lib: avoid recompilation of anonymous functions

Since at least V8 5.4, using function.bind() is now fast enough to
use to avoid recompiling/reoptimizing the same anonymous functions.
These changes especially impact http servers.

PR-URL: #6533
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

lib/_http_outgoing.js

@@ -545,6 +545,9 @@ OutgoingMessage.prototype.addTrailers = function addTrailers(headers) {
 
 const crlf_buf = Buffer.from('\r\n');
 
+function onFinish(outmsg) {
+  outmsg.emit('finish');
+}
 
 OutgoingMessage.prototype.end = function end(data, encoding, callback) {
   if (typeof data === 'function') {
@@ -592,9 +595,7 @@ OutgoingMessage.prototype.end = function end(data, encoding, callback) {
   if (typeof callback === 'function')
     this.once('finish', callback);
 
-  const finish = () => {
-    this.emit('finish');
-  };
+  var finish = onFinish.bind(undefined, this);
 
   var ret;
   if (this._hasBody && this.chunkedEncoding) {

lib/_stream_writable.js

@@ -86,9 +86,7 @@ function WritableState(options, stream) {
   this.bufferProcessing = false;
 
   // the callback that's passed to _write(chunk,cb)
-  this.onwrite = function(er) {
-    onwrite(stream, er);
-  };
+  this.onwrite = onwrite.bind(undefined, stream);
 
   // the callback that the user supplies to write(chunk,encoding,cb)
   this.writecb = null;
@@ -538,20 +536,21 @@ function endWritable(stream, state, cb) {
 function CorkedRequest(state) {
   this.next = null;
   this.entry = null;
+  this.finish = onCorkedFinish.bind(undefined, this, state);
+}
 
-  this.finish = (err) => {
-    var entry = this.entry;
-    this.entry = null;
-    while (entry) {
-      var cb = entry.callback;
-      state.pendingcb--;
-      cb(err);
-      entry = entry.next;
-    }
-    if (state.corkedRequestsFree) {
-      state.corkedRequestsFree.next = this;
-    } else {
-      state.corkedRequestsFree = this;
-    }
-  };
+function onCorkedFinish(corkReq, state, err) {
+  var entry = corkReq.entry;
+  corkReq.entry = null;
+  while (entry) {
+    var cb = entry.callback;
+    state.pendingcb--;
+    cb(err);
+    entry = entry.next;
+  }
+  if (state.corkedRequestsFree) {
+    state.corkedRequestsFree.next = corkReq;
+  } else {
+    state.corkedRequestsFree = corkReq;
+  }
 }