Split convertIf into an AST part and IR part.

Change-Id: I14205773c5934cfc1896be48783818ff096e71c2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/352504
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
2 files changed