SkSharedMutex::acquire to check thread state.

This makes SkSharedMutex::acquire() assert if a thread has already
acquired a shared lock.

Change-Id: I35a186a137b9efcad1132093e1bb18c8822e1538
Reviewed-on: https://skia-review.googlesource.com/128160
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Herb Derby <herb@google.com>
1 file changed