Sk4px blit mask.

Sk4px blit mask.

Local SKP nanobenching ranges SSE between 1.05x and 0.87x, much more heavily weighted toward <1.0x ratios (speedups).
I profiled the top five regressions (1.05x-1.01x) and they look like noise.  Will follow up after broad bot results.

NEON looks similar but less extreme than SSE changes, ranging between 1.02x and 0.95x, again mostly speedups in 0.99x-0.97x range.

The old code trifurcated into black, opaque-but-not-black, and general versions as a function of the constant src color.  I did not see a significant difference between general and opaque-but-not-black, and I don't think a black version would be faster using SIMD.  So we have here just one version of the code, the general version.

Somewhat fantastically, I see no pixel diffs on GMs or SKPs.

I will be following up with more CLs for the other procs called by SkBlitMask.
BUG=skia:

Committed: https://skia.googlesource.com/skia/+/4977983510028712528743aa877f6da83781b381

[mtklein_C, 2015-08-10 18:59:04]

The CQ bit was checked by mtklein@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-10 18:59:17]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1278253003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1278253003/20001

[mtklein_C, 2015-08-10 19:05:19]

The CQ bit was checked by mtklein@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-10 19:05:27]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1278253003/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1278253003/40001

[mtklein_C, 2015-08-10 19:08:22]

mtklein@chromium.org changed reviewers:
+ reed@google.com

[commit-bot: I haz the power, 2015-08-10 19:20:18]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-10 19:20:19]

Dry run: This issue passed the CQ dry run.

[reed1, 2015-08-10 19:44:16]

lgtm

[mtklein_C, 2015-08-10 19:49:41]

The CQ bit was checked by mtklein@chromium.org

[mtklein_C, 2015-08-10 19:49:41]

The patchset sent to the CQ was uploaded after l-g-t-m from reed@google.com
Link to the patchset: https://codereview.chromium.org/1278253003/#ps60001
(title: "note overflow")

[commit-bot: I haz the power, 2015-08-10 19:49:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1278253003/60001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1278253003/60001

[commit-bot: I haz the power, 2015-08-10 19:58:21]

Committed patchset #4 (id:60001) as
https://skia.googlesource.com/skia/+/4977983510028712528743aa877f6da83781b381