add more tests for SkCubicMap

Bug: skia:
Change-Id: I75e582a4486abbccf081f77457895c3da93fea16
Reviewed-on: https://skia-review.googlesource.com/147219
Auto-Submit: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
2 files changed