Combined approach.

Combined approach.

This combines some ideas from these two CLs:
    - try stosd/w
    - update memset16/32 inlining heuristics


BUG=skia:4316
Blinking in and out for perf.skia.org.
TBR=reed@google.com

Committed: https://skia.googlesource.com/skia/+/46243a7c02a1d5116e55a27ff59218f9c320df97

Possible that MSAN doesn't understand rep sto, or that there's a bug here:
http://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20ChromeOS%20MSan%20Tests/builds/4178/steps/cc_unittests/logs/IntersectingQuadPixelTest_1.RenderPassQuads

[mtklein_C, 2015-09-21 17:44:51]

The CQ bit was checked by mtklein@chromium.org

[commit-bot: I haz the power, 2015-09-21 17:45:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1356133002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1356133002/1

[commit-bot: I haz the power, 2015-09-21 17:45:50]

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

[commit-bot: I haz the power, 2015-09-21 17:45:51]

Try jobs failed on following builders:
  Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-Trybot on client.skia (JOB_FAILED,
http://build.chromium.org/p/client.skia/builders/Test-Ubuntu-GCC-GCE-CPU-AVX2...)
  Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-Shared-Trybot on client.skia
(JOB_FAILED,
http://build.chromium.org/p/client.skia/builders/Test-Ubuntu-GCC-GCE-CPU-AVX2...)
  Build-Ubuntu-GCC-x86_64-Release-Trybot on client.skia.compile (JOB_FAILED,
http://build.chromium.org/p/client.skia.compile/builders/Build-Ubuntu-GCC-x86...)

[mtklein_C, 2015-09-21 17:46:11]

The CQ bit was checked by mtklein@chromium.org

[commit-bot: I haz the power, 2015-09-21 17:46:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1356133002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1356133002/20001

[mtklein_C, 2015-09-21 17:50:02]

The CQ bit was unchecked by mtklein@chromium.org

[mtklein_C, 2015-09-21 17:50:05]

The CQ bit was checked by mtklein@chromium.org

[commit-bot: I haz the power, 2015-09-21 17:50:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1356133002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1356133002/20001

[commit-bot: I haz the power, 2015-09-21 17:50:59]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/46243a7c02a1d5116e55a27ff59218f9c320df97

[mtklein, 2015-09-21 18:02:22]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/1353703006/ by mtklein@google.com.

The reason for reverting is: whee.