remove sk_atomic_compare_exchange

Whatever nonsense SkPicture::uniqueID() was doing, it doesn't
need to do it.  It can just get its unique ID normally.

I've ported SkEventTracer in the straightforward way.

Change-Id: I103e7e05258ad49e1e3f333fc907f039cef3f8c9
Reviewed-on: https://skia-review.googlesource.com/c/174280
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
4 files changed