Maybe fix issue #28457907: Pebble app crash + reboot

Fix this long-standing multi-threading issue in Bundle
when multiple threads are trying to read from a Bundle
and conflict to due unparceling.

There are two critical sections this protects: writing
the bundle in to a parcel (when it is doing this from
the bundle's already parcelled representation), and
unparcelling a bundle into its map of entries.

Change-Id: I5470002f090e63dd623a573da6c204d3b5b661f4