Add a real SkXbyak bench, implement enough to run it.

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD

SkXbyak_…
9320  …JITCompiled 1x  …Interpreted 1.24x  …HandWritten 2.5x

Change-Id: I37d2d255ff32dcce73d29081d506e2d67477af97
Reviewed-on: https://skia-review.googlesource.com/6697
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Herb Derby <herb@google.com>
4 files changed