This merges and refactors SkAtomics.h and SkBarriers.h into SkAtomics.h and
some ports/ implementations. The major new feature is that we can express
memory orders explicitly rather than only through comments.
The porting layer is reduced to four template functions:
- sk_atomic_load
- sk_atomic_store
- sk_atomic_fetch_add
- sk_atomic_compare_exchange
From those four we can reconstruct all our previous sk_atomic_foo.
There are three ports:
- SkAtomics_std: uses C++11 <atomic>, used with MSVC
- SkAtomics_atomic: uses newer GCC/Clang intrinsics, used on not-MSVC where possible
- SkAtomics_sync: uses older GCC/Clang intrinsics, used where SkAtomics_atomic not supported
No public API changes.
TBR=reed@google.com
BUG=skia:
Review URL: https://codereview.chromium.org/896553002
