Add more timers for codegen time.

We're seeing high time in codegen while investigating workloads with high concurrency.

Change-Id: I7f25a2ef82fd80f40efe1dd909505b6419020782
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5094
Reviewed-by: Nong Li <nong@cloudera.com>
Tested-by: jenkins