Simplify implementation of SkOnce to not need so many comments.

Simplify implementation of SkOnce to not need so many comments.

I think this version reads more clearly, and the key invariants are
expressed in code rather than comments:
   - race losers always go through an acquire
   - we never exit the function unless fState is Done

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1951013004

Committed: https://skia.googlesource.com/skia/+/b37c68ad42ae7880e702649a01655165c7e12acc

[mtklein_C, 2016-05-04 20:15:38]

Description was changed from

==========
Simplify implementation of SkOnce to not need so many comments.

I think this version reads more clearly, and the key invariants are
expressed in code rather than comments:
   - race losers always go through an acquire
   - we never exit the function unless fState is Done

BUG=skia:
==========

to

==========
Simplify implementation of SkOnce to not need so many comments.

I think this version reads more clearly, and the key invariants are
expressed in code rather than comments:
   - race losers always go through an acquire
   - we never exit the function unless fState is Done

BUG=skia:
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...
==========

[mtklein_C, 2016-05-04 20:16:57]

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

[commit-bot: I haz the power, 2016-05-04 20:17:03]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1951013004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1951013004/1

[mtklein_C, 2016-05-04 20:24:36]

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

[commit-bot: I haz the power, 2016-05-04 20:32:14]

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

[commit-bot: I haz the power, 2016-05-04 20:32:15]

Dry run: This issue passed the CQ dry run.

[reed1, 2016-05-04 20:50:27]

reed@google.com changed reviewers:
+ reed@google.com

[reed1, 2016-05-04 20:50:28]

lgtm

[mtklein, 2016-05-04 20:56:31]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2016-05-04 20:56:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1951013004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1951013004/1

[commit-bot: I haz the power, 2016-05-04 20:57:32]

Description was changed from

==========
Simplify implementation of SkOnce to not need so many comments.

I think this version reads more clearly, and the key invariants are
expressed in code rather than comments:
   - race losers always go through an acquire
   - we never exit the function unless fState is Done

BUG=skia:
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...
==========

to

==========
Simplify implementation of SkOnce to not need so many comments.

I think this version reads more clearly, and the key invariants are
expressed in code rather than comments:
   - race losers always go through an acquire
   - we never exit the function unless fState is Done

BUG=skia:
GOLD_TRYBOT_URL=
https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&is...

Committed:
https://skia.googlesource.com/skia/+/b37c68ad42ae7880e702649a01655165c7e12acc
==========

[commit-bot: I haz the power, 2016-05-04 20:57:33]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/b37c68ad42ae7880e702649a01655165c7e12acc