Remove hack allowing fRefCnt of 0.

In some legacy situations users of SkRefCnt subclasses were keeping
the objects alive with a reference count of 0. Now that these users are
cleaned up, remove the hack which allowed such code to keep functioning.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3264

Change-Id: I22f63d87b6d995cad6326998284930ad9eaa2983
Reviewed-on: https://skia-review.googlesource.com/3264
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
1 file changed