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

Performance Gain (vs C auto-vectorized)
ARGBToYJRow_MSA       - ~3.2x
ARGBToYJRow_Any_MSA   - ~2.7x
BGRAToYRow_MSA        - ~3.2x
BGRAToYRow_Any_MSA    - ~2.7x
ABGRToYRow_MSA        - ~3.2x
ABGRToYRow_Any_MSA    - ~2.6x
RGBAToYRow_MSA        - ~3.1x
RGBAToYRow_Any_MSA    - ~2.7x
ARGBToUVJRow_MSA      - ~5.5x
ARGBToUVJRow_Any_MSA  - ~4.5x
BGRAToUVRow_MSA       - ~2.1x
BGRAToUVRow_Any_MSA   - ~2.0x
ABGRToUVRow_MSA       - ~2.1x
ABGRToUVRow_Any_MSA   - ~1.9x
RGBAToUVRow_MSA       - ~2.2x
RGBAToUVRow_Any_MSA   - ~1.9x

Performance Gain (vs C non-vectorized)
ARGBToYJRow_MSA       - ~10.9x
ARGBToYJRow_Any_MSA   -  ~9.2x
BGRAToYRow_MSA        - ~10.9x
BGRAToYRow_Any_MSA    -  ~9.3x
ABGRToYRow_MSA        - ~11.0x
ABGRToYRow_Any_MSA    -  ~9.3x
RGBAToYRow_MSA        - ~10.9x
RGBAToYRow_Any_MSA    -  ~9.1x
ARGBToUVJRow_MSA      - ~12.4x
ARGBToUVJRow_Any_MSA  - ~10.5x
BGRAToUVRow_MSA       -  ~4.7x
BGRAToUVRow_Any_MSA   -  ~4.4x
ABGRToUVRow_MSA       -  ~4.7x
ABGRToUVRow_Any_MSA   -  ~4.5x
RGBAToUVRow_MSA       -  ~4.8x
RGBAToUVRow_Any_MSA   -  ~4.4x

Review-Url: https://codereview.chromium.org/2641153003 .