Outline SkSpinlock::acquire().

The proportion of time spent doing useful work is well over 99% in acquire(),
so outlining it doesn't hurt speed at all, and makes it much easier to pick out
on a profile.

It'd be about 50/50 work/overhead if we outlined the extremely-cheap release().
I also tried outlining some SkRefCnt methods with similar mixed results.

BUG=skia:

No public API changes.
TBR=reed@google.com

Review URL: https://codereview.chromium.org/1212253013
3 files changed