disconnected.
To restore Document IDs when the device is reconnected, we need to keep
the metadata in database so that we can use it as hint to remap document
ID with new MTP IDs.
BUG=26212981
Change-Id: Idcc93c41c09d082a709281022c56188dabc80515
(cherry picked from commit 53f5af3f2ba1328d301a0f8a4ae3f574ccc5da65)