Reimplement NV21ToARGB to allow different color matrix.

Reimplement NV21ToARGB to allow different color matrix.

Low level for NV21ToARGB written to accept yuv matrix used by
other YUV to ARGB functions.
Previously NV21 was implemented for Windows using NV12 with a different
matrix that swapped U and V.  But the Arm version of the low level does
not allow the matrix U and V contributions to be swapped.
Using a new low level function that reads NV21 and uses the same
yuvconstants as other YUV conversion functions allows an Arm port of
this function.

TBR=harryjin@google.com
BUG=libyuv:500
Committed: https://chromium.googlesource.com/libyuv/libyuv/+/914a9856c7e6cab17f9d923119e043947f5aa58c

[fbarchard, 2015-10-07 03:32:14]

fbarchard@chromium.org changed reviewers:
+ harrym@chromium.org

[fbarchard, 2015-10-07 03:32:34]

fbarchard@chromium.org changed reviewers:
+ jarryjin@google.com
- harrym@chromium.org

[fbarchard, 2015-10-07 03:32:57]

fbarchard@chromium.org changed reviewers:
+ harryjin@google.com
- jarryjin@google.com

[fbarchard, 2015-10-07 03:34:32]

win64 llvm version
NV12ToARGB_Any (582 ms)
NV21ToARGB_Invert (550 ms)
NV21ToARGB_Unaligned (515 ms)
NV12ToARGB_Unaligned (502 ms)
NV21ToARGB_Any (492 ms)
NV12ToARGB_Invert (454 ms)
NV21ToARGB_Opt (436 ms)
NV12ToARGB_Opt (421 ms)

[fbarchard1, 2015-10-07 03:34:49]

Committed patchset #3 (id:40001) manually as
914a9856c7e6cab17f9d923119e043947f5aa58c (presubmit successful).

[harryjin, 2015-10-07 05:30:48]

lgtm