- Use std::atomic directly.
- No more need for SkPODSpinlock or SK_DECLARE_STATIC_SPINLOCK.
Now simple code like this works as you'd hope:
static SkSpinlock gLock;
That is, it starts unlocked and there's no static initializer.
std::atomic_flag would make this terser and standard-guaranteed,
but ATOMIC_FLAG_INIT caused not-yet-implemented errors on MSVC 2013.
The generated code for this approach is identical.
It appears the implicit constructor is constexpr when all the member
initializers are. I'm hoping this way of producing constexpr constructors
without typing "constexpr" gives us a way to eliminate more SkFoo / SkBaseFoo
distinctions and SK_DECLARE_STATIC_FOO. This was certainly the easiest.
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1734383002
Review URL: https://codereview.chromium.org/1734383002
