Migrate EliminateUnreachableCode into Transform.

Change-Id: Ib32895a78a8de4c49ce1208f0c1b9b111d092b42
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/456643
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
7 files changed