Using type-tags for test SingletonVaults
Summary: This makes test SingletonVaults more similar to global SingletonVault. It also ensures that every SingletonVault is a singleton, which allows potential optimization of making each SingletonEntry a Singleton too, which itself will make get/get_weak as efficient as get_fast/get_weak_fast.
Test Plan: unit test
Reviewed By: chip@fb.com
Subscribers: folly-diffs@, yfeldblum
FB internal diff:
D1823663
Signature: t1:
1823663:
1423188884:
4ab2b47cfba270a66613f6f2458b6affc0ed96ad