Add instrumentation for BackupManager during restore.

This CL adds more instumentation to
backup/restore operation in the BackupManager. For more details please
point to:
https://docs.google.com/document/d/1sUboR28LjkT1wRXOwVOV3tLo0qisiCvzxIGmzCVEjbI/edit#
This first Cl introduces 3 events that we sent to the monitor.
The base cl is ag/1835775

Test: TODO

BUG: 34873525
Change-Id: I127fe739a7522078eecce2ae689a4607203a98da