Patch up ref counting of proxies (take 2)

TBR=bsalomon@google.com
Change-Id: I2376c6b17ac7c2b28837bafb76583934ab72558e
Reviewed-on: https://skia-review.googlesource.com/70501
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
3 files changed