On Pixel 3
Was
BM_ConvertToGray/1280/720/3                        2360958 ns      2334984 ns         2999
BM_ConvertToGray/1279/721/3                        2360289 ns      2334329 ns         2994
BM_ConvertGrayTensorflowCoefficients/1280/720/3    2983296 ns      2947113 ns         2259
BM_ConvertGrayTensorflowCoefficients/1279/721/3    2871205 ns      2835359 ns         2170

Now
BM_ConvertToGray/1280/720/3                        2358469 ns      2334068 ns         2997
BM_ConvertToGray/1279/721/3                        2364584 ns      2336892 ns         2995
BM_ConvertGrayTensorflowCoefficients/1280/720/3     281312 ns       278244 ns        25170
BM_ConvertGrayTensorflowCoefficients/1279/721/3     351310 ns       347229 ns        20217

BUG=libyuv:854

Change-Id: If2192affc2d3219e0fb824737d75b9374a25d709
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/2003236
Commit-Queue: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: richard winterton <rrwinterton@gmail.com>