The API and implementation are very much simplified.
You may not want to bother reading the diff.
As is our trend, SkOnce now uses <atomic> directly.
Member initialization means we don't need SK_DECLARE_STATIC_ONCE.
SkSpinlock already works this same way.
All uses of the old API taking an external bool* and Lock* were pessimal,
so I have not carried this sort of API forward. It's simpler, faster,
and more space-efficient to always use this single SkOnce class interface.
SkOnce weighs 2 bytes: a done bool and an SkSpinlock, also a bool internally.
This API refactoring opens up the opportunity to fuse those into a single
three-state byte if we'd like.
No public API changes.
TBR=reed@google.com
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1894893002
Review URL: https://codereview.chromium.org/1894893002
d9dd428211