A sanity check that H010ToARGB is doing the correct math.
The normal test only checks the C and ASM match, but they could
both be wrong, or the common code could be wrong.
This test checks a grey scale ramp matches expected results.

Bug: libyuv:751
Test: LibYUVConvertTest.TestH420ToARGB and LibYUVConvertTest.TestH010ToARGB
Change-Id: Ie8c2b91ac9993f41675c02d0dde9db72d0612450
Reviewed-on: https://chromium-review.googlesource.com/851474Reviewed-by: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Frank Barchard <fbarchard@chromium.org>