R=fbarchard@google.com
BUG=libyuv:634

Performance Gains :- (vs C vectorized)

I422ToARGBRow_MSA     : ~1.6x
I422ToRGBARow_MSA     : ~1.6x

I422ToARGBRow_Any_MSA : ~1.58x
I422ToRGBARow_Any_MSA : ~1.6x

Performance Gains :- (vs C non-vectorized)

I422ToARGBRow_MSA     : ~7x
I422ToRGBARow_MSA     : ~7x

I422ToARGBRow_Any_MSA : ~6.9x
I422ToRGBARow_Any_MSA : ~6.8x

Regarding performance measurement, We have created standalone tests which pass in row's data from a 1920x1080 filled buffer to both the C and MSA functions. And such N iterations are executed to get more accurate timings of C vs MSA.

Review URL: https://codereview.chromium.org/2430313005 .