SoLoader- expose loaded libraries publicly
SoLoader- expose loaded libraries publicly

Summary: This change has no functional impact. It just adds a getter and changes a field from Set to HashSet.

Differential Revision: D7623930

fbshipit-source-id: 8e92c2478e2660dbaa8837f656e653f2810e0f2b

facebook/SoLoader,facebook/SoLoader,facebook/SoLoader