Multi-threaded strike cache

Allow multiple threads to share the same strike. The old
system of removing the cache from the linked list is no longer.
The strikes stay in the list and can be found by other threads.

* Removed strike size verification. There was no way to get the
locks to work out. The whole point of the change was to have multiple
threads muting the structure at the same time.

* Strikes are now refed instead of being checked out. Therefore,
ExclusiveStrikePtr is now just wraps an sk_sp, and should be renamed
in a future CL.

Change-Id: I832642332a3106e30745f9cdd3156ae72d41fd0b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/272057
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
5 files changed