namespace {} trick for SK_DECLARE_STATIC_ONCE

Like all our other SK_DECLARE_STATIC_*, it's usually not a thread-safe
thing to put inside a function.  Adding namespace {} prevents that
syntactically.

Needs https://codereview.chromium.org/841263004/ to land first.

BUG=chromium:447890

No public API changes.
TBR=reed@google.com

Review URL: https://codereview.chromium.org/806473006
6 files changed