Create debug only SkSingleOwner

This is so Gpu code can guard against improper multithreaded usage in
debug builds

TBR=bsalomon@google.com
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1555953004

Review URL: https://codereview.chromium.org/1555953004
6 files changed