Optimize away IOBuf clones on hot path
Optimize away IOBuf clones on hot path

Summary:
'get' is the most frequent memcached operation. On a get reply, we should go to heap
as little as possible.  This diff optimizes for this scenario, where replies
have only one IOBuf field.

Reviewed By: pavlo-fb

Differential Revision: D3226592

fb-gh-sync-id: 92e1a1fac5735bd268691cf11990a96ae6fa8309
fbshipit-source-id: 92e1a1fac5735bd268691cf11990a96ae6fa8309

LinusU/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,facebook/fbthrift,getyourguide/fbthrift,facebook/fbthrift,getyourguide/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,LinusU/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,facebook/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,facebook/fbthrift,getyourguide/fbthrift,LinusU/fbthrift