http: eliminate capture of ClientRequest in Agent

Keepalive sockets that are returned to the agent's freesocket pool were
previously capturing a reference to the ClientRequest that initiated the
request.
This commit eliminates that by moving the installation of the socket
listeners to a different function.
Backport-PR-URL: #15500
PR-URL: #10134
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: Evan Torrie

lib/_http_agent.js

@@ -206,37 +206,41 @@ Agent.prototype.createSocket = function(req, options, cb) {
 }
 self.sockets[name].push(s);
 debug('sockets',name,self.sockets[name].length);
-
-functiononFree(){
-self.emit('free',s,options);
-}
-s.on('free',onFree);
-
-functiononClose(err){
-debug('CLIENT socket onClose');
-// This is the only place where sockets get removed from the Agent.
-// If you want to remove a socket from the pool, just close it.
-// All socket errors end in a close event anyway.
-self.removeSocket(s,options);
-}
-s.on('close',onClose);
-
-functiononRemove(){
-// We need this function for cases like HTTP 'upgrade'
-// (defined by WebSockets) where we need to remove a socket from the
-// pool because it'll be locked up indefinitely
-debug('CLIENT socket onRemove');
-self.removeSocket(s,options);
-s.removeListener('close',onClose);
-s.removeListener('free',onFree);
-s.removeListener('agentRemove',onRemove);
-}
-s.on('agentRemove',onRemove);
+installListeners(self,s,options);
 cb(null,s);
 }
 };
 
-Agent.prototype.removeSocket=function(s,options){
+functioninstallListeners(agent,s,options){
+functiononFree(){
+debug('CLIENT socket onFree');
+agent.emit('free',s,options);
+}
+s.on('free',onFree);
+
+functiononClose(err){
+debug('CLIENT socket onClose');
+// This is the only place where sockets get removed from the Agent.
+// If you want to remove a socket from the pool, just close it.
+// All socket errors end in a close event anyway.
+agent.removeSocket(s,options);
+}
+s.on('close',onClose);
+
+functiononRemove(){
+// We need this function for cases like HTTP 'upgrade'
+// (defined by WebSockets) where we need to remove a socket from the
+// pool because it'll be locked up indefinitely
+debug('CLIENT socket onRemove');
+agent.removeSocket(s,options);
+s.removeListener('close',onClose);
+s.removeListener('free',onFree);
+s.removeListener('agentRemove',onRemove);
+}
+s.on('agentRemove',onRemove);
+}
+
+Agent.prototype.removeSocket=functionremoveSocket(s,options){
 varname=this.getName(options);
 debug('removeSocket',name,'writable:',s.writable);
 varsets=[this.sockets];