Add Round() to DSL.

I wrote some code which needed Round(); it isn't in ES2 so it wasn't in
the DSL intrinsic set yet.

Change-Id: I304f61b502a68d255d15899181e34fcae2ef16a0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/447017
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
3 files changed