Disable F16-nullptr sources

Also includes the refactor that triggered this change - stricter
checking on creation on raster SkImages.

Bug: skia:
Change-Id: Ie3216ac3f5307de4b78792b472676faa51e5459d
Reviewed-on: https://skia-review.googlesource.com/19040
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
4 files changed