Add checkbox to Viewer to force-enable Runtime Blends.

In a perfect world, this should always render the same, just perhaps a
bit more slowly.

Change-Id: I750ad43142d4d192be4db7396989d978025179a8
Bug: skia:12080
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/429101
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed