Add test demonstrating overflow error in SkSL.

Change-Id: Ic6a3ce722c607d4d3c47d37e5749a01ae5fb193f
Bug: skia:12050
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/412668
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>
5 files changed