[NAN] Refactor session lifecycle to clarify API & eliminate race conditions [DO NOT MERGE]

Bug: 27257965
Change-Id: I405de3d18187770d97171d636abddfe4e1be4510
8 files changed
tree: dcd8bb1fb24fb50a50354da315d5ef91ddffd27d
  1. service/
  2. tests/