Add checkbox to disable Shadertoy uniform support.

Generally these are harmless, but in some cases, they get in the way.
(e.g. when trying to make a minimal debug trace)

Change-Id: I2218e68c70fdbf85c3e10df232955038e2aaed29
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/488376
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed