Add test for Runtime Effects and narrowing conversions.

This code intentionally mixes half4s and float4s everywhere. Before
http://review.skia.org/435916 landed, this resulted in a compile error.

Change-Id: I852fef6ee99a8b78623e0e9ddeee2ad84a8c0504
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/436058
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>
4 files changed