Previously H010ToAR30 was done in a 3 step conversion:
H010ToH420, H420ToARGB, ARGBToAR30.
This CL merges the first 2 steps into H010ToARGB, to
improve performance.
Caveat - only 10 bit YUV is supported at this time.
Previously the low level code supported different numbers
of bits - 9, 10, 12 or 16.

Was 3 step conversion:
LibYUVConvertTest.H010ToAR30_Any (1263 ms)
LibYUVConvertTest.H010ToAR30_Unaligned (951 ms)
LibYUVConvertTest.H010ToAR30_Invert (913 ms)
LibYUVConvertTest.H010ToAR30_Opt (901 ms)

Now 2 step conversion:
LibYUVConvertTest.H010ToAR30_Any (853 ms)
LibYUVConvertTest.H010ToAR30_Unaligned (811 ms)
LibYUVConvertTest.H010ToAR30_Invert (781 ms)
LibYUVConvertTest.H010ToAR30_Opt (755 ms)

Bug: libyuv:751
Test: LibYUVConvertTest.H010ToAR30_Opt
Change-Id: Ica7574040401cd57145a4827acdf3c0e58346a2a
Reviewed-on: https://chromium-review.googlesource.com/853288Reviewed-by: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>