Add Viewer checkbox to toggle Control-Flow Analysis.

This gives Viewer a way to dynamically toggle CFA off and on, so we can
immediately see the impact on shader optimization.

Change-Id: I912df70de126a74a1f0d11c511b2acc64f1e9f28
Bug: skia:11319
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/380456
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
3 files changed