Merge "Allocate code generators on the arena." am: 38e398b am: 78203b1
am: 3e49f36

* commit '3e49f369e4b1c47a91e7d41ae8b2884fe3882633':
  Allocate code generators on the arena.

Change-Id: I3e78242f6016dcb2a0bf000345963c4dc8eb1aad