ARM I420AlphaToABGR_Opt optimize for Neon

[GoogleCodeExporter]

I420AlphaToARGB_Opt is using C code on Arm.  Optimize for Neon.

runyuva10 ConvertTest*I420*ToA???_*

util/android/test_runner.py gtest -s libyuv_unittest -t 7200 --verbose 
--release --gtest_filter=*ConvertTest*I420*ToA???_* -a "--libyuv_width=1280 
--libyuv_height=720 --libyuv_repeat=999 --libyuv_flags=-1"

I420AlphaToARGB_Premult (77882 ms)
I420AlphaToABGR_Premult (77382 ms)
I420AlphaToARGB_Invert (76718 ms)
I420AlphaToARGB_Unaligned (76620 ms)
I420AlphaToARGB_Opt (76488 ms)
I420AlphaToARGB_Any (76200 ms)
I420AlphaToABGR_Opt (74689 ms)
I420AlphaToABGR_Any (74684 ms)
I420AlphaToABGR_Invert (74532 ms)
I420AlphaToABGR_Unaligned (74470 ms)
I420ToARGB_Unaligned (3966 ms)
I420ToABGR_Any (3649 ms)
I420ToARGB_Any (3635 ms)
I420ToABGR_Invert (3547 ms)
I420ToABGR_Unaligned (3504 ms)
I420ToABGR_Opt (3370 ms)
I420ToARGB_Invert (3364 ms)
I420ToARGB_Opt (3304 ms)

Original issue reported on code.google.com by fbarch...@chromium.org on 26 Oct 2015 at 10:15