A given object may be unique, but its owner may not be unique
and another thread may ref the object via the owner at any time.
This happens e.g. when sharing SkPictures between threads.
Bug: skia:10286
Change-Id: I51b5239338a81aaa4d67db05f01f2c7c24182096
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/376619
Reviewed-by: Ben Wagner <bungeman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Adlai Holler <adlai@google.com>
dc8a6b64cc