Add a new Program input indicating that dFdy() is used.

Change-Id: I87811860c3fb30682923c68cc2c5d8336b3d38e6
Bug: skia:12064
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/414516
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
3 files changed