decs/examples: Support more fiddle types: offscreen, srgb

Change-Id: I606eb7dfbce04147bfc6e287bb2c75051a44a076
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/264692
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
9 files changed