This reverts commit cfdc07aa0e.
Reason for revert: nope, flutter windows bots don't have it. we got caught.
Original change's description:
> replace SkSharedMutex
>
> I am debugging an issue with SkSharedMutex and noticed
> how sparsely it is used. That got me curious to see if
> we can replace it with a std::shared_mutex (from C++17).
>
> Bug: skia:10177
> Change-Id: I1ce4d2a5897af198d6ae5fb850548ff917a58f50
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/285691
> Reviewed-by: Ben Wagner <bungeman@google.com>
> Commit-Queue: Mike Klein <mtklein@google.com>
TBR=mtklein@google.com,bungeman@google.com,herb@google.com
Change-Id: Iab4e55d749e386233ff0e2ba2c1cd10d5e6f1615
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:10177
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/286124
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
77083c7d74