Make pending count optional
Make pending count optional

Summary: Since everything happens in IO threads, it was hard to get a real request count.  This feature can be expensive with lots of connections

Test Plan: unit tests

Reviewed By: mshneer@fb.com, alandau@fb.com

Subscribers: fugalh, trunkagent, doug, lars, alandau, bmatheny, xie, mshneer, vloh

FB internal diff: D1662840

Tasks: 5552958

Signature: t1:1662840:1415255196:c3ae4ea74a45b37f7dac15ecc354bbc2bcc94156

Orvid/fbthrift,SergeyMakarenko/fbthrift,maxwell-demon/fbthrift,LinusU/fbthrift,jesboat/fbthrift,jesboat/fbthrift,SergeyMakarenko/fbthrift,soumith/fbthrift,jesboat/fbthrift,kangkot/fbthrift,LinusU/fbthrift,uber/fbthrift,fengshao0907/fbthrift,SergeyMakarenko/fbthrift,Orvid/fbthrift,kangkot/fbthrift,uber/fbthrift,project-zerus/fbthrift,guker/fbthrift,kangkot/fbthrift,getyourguide/fbthrift,uber/fbthrift,maxwell-demon/fbthrift,SergeyMakarenko/fbthrift,project-zerus/fbthrift,jesboat/fbthrift,maxwell-demon/fbthrift,jesboat/fbthrift,LinusU/fbthrift,Orvid/fbthrift,uber/fbthrift,soumith/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,jesboat/fbthrift,maxwell-demon/fbthrift,uber/fbthrift,maxwell-demon/fbthrift,uber/fbthrift,SergeyMakarenko/fbthrift,chjp2046/fbthrift,soumith/fbthrift,raphaelamorim/fbthrift,soumith/fbthrift,chjp2046/fbthrift,chjp2046/fbthrift,fengshao0907/fbthrift,guker/fbthrift,soumith/fbthrift,project-zerus/fbthrift,project-zerus/fbthrift,kangkot/fbthrift,chjp2046/fbthrift,sinjar666/fbthrift,soumith/fbthrift,sinjar666/fbthrift,guker/fbthrift,uber/fbthrift,project-zerus/fbthrift,project-zerus/fbthrift,HankFaan/fbthrift,LinusU/fbthrift,Orvid/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,soumith/fbthrift,raphaelamorim/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,facebook/fbthrift,HankFaan/fbthrift,kangkot/fbthrift,SergeyMakarenko/fbthrift,guker/fbthrift,getyourguide/fbthrift,raphaelamorim/fbthrift,guker/fbthrift,HankFaan/fbthrift,guker/fbthrift,jesboat/fbthrift,facebook/fbthrift,getyourguide/fbthrift,HankFaan/fbthrift,LinusU/fbthrift,project-zerus/fbthrift,getyourguide/fbthrift,maxwell-demon/fbthrift,Orvid/fbthrift,jesboat/fbthrift,sinjar666/fbthrift,maxwell-demon/fbthrift,fengshao0907/fbthrift,uber/fbthrift,fengshao0907/fbthrift,fengshao0907/fbthrift,guker/fbthrift,Orvid/fbthrift,fengshao0907/fbthrift,kangkot/fbthrift,HankFaan/fbthrift,guker/fbthrift,raphaelamorim/fbthrift,fengshao0907/fbthrift,chjp2046/fbthrift,sinjar666/fbthrift,getyourguide/fbthrift,Orvid/fbthrift,kangkot/fbthrift,kangkot/fbthrift,raphaelamorim/fbthrift,jesboat/fbthrift,kangkot/fbthrift,fengshao0907/fbthrift,raphaelamorim/fbthrift,soumith/fbthrift,project-zerus/fbthrift,uber/fbthrift,sinjar666/fbthrift,chjp2046/fbthrift,guker/fbthrift,HankFaan/fbthrift,jesboat/fbthrift,raphaelamorim/fbthrift,SergeyMakarenko/fbthrift,jesboat/fbthrift,getyourguide/fbthrift,chjp2046/fbthrift,sinjar666/fbthrift,sinjar666/fbthrift,HankFaan/fbthrift,sinjar666/fbthrift,project-zerus/fbthrift,maxwell-demon/fbthrift,guker/fbthrift,soumith/fbthrift,kangkot/fbthrift,fengshao0907/fbthrift,getyourguide/fbthrift,uber/fbthrift,raphaelamorim/fbthrift,chjp2046/fbthrift,HankFaan/fbthrift,Orvid/fbthrift,raphaelamorim/fbthrift,jesboat/fbthrift,maxwell-demon/fbthrift,HankFaan/fbthrift,SergeyMakarenko/fbthrift,chjp2046/fbthrift,project-zerus/fbthrift,LinusU/fbthrift,soumith/fbthrift,chjp2046/fbthrift,raphaelamorim/fbthrift,LinusU/fbthrift,fengshao0907/fbthrift,uber/fbthrift,fengshao0907/fbthrift,LinusU/fbthrift,facebook/fbthrift,sinjar666/fbthrift,LinusU/fbthrift,maxwell-demon/fbthrift,chjp2046/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,project-zerus/fbthrift,Orvid/fbthrift,facebook/fbthrift,HankFaan/fbthrift,getyourguide/fbthrift,raphaelamorim/fbthrift,Orvid/fbthrift,kangkot/fbthrift,maxwell-demon/fbthrift,sinjar666/fbthrift,LinusU/fbthrift,sinjar666/fbthrift,getyourguide/fbthrift,guker/fbthrift,facebook/fbthrift,soumith/fbthrift,chjp2046/fbthrift,uber/fbthrift,Orvid/fbthrift,HankFaan/fbthrift,facebook/fbthrift,project-zerus/fbthrift,facebook/fbthrift