[RefactoredBMS] Eliminate a race condition that could lead to
calling PBT#finalizeBackup() twice

This CL replicates ag/2510127 in RefactoredBMS.

Test: runtest -p com.android.server.backup frameworks-services
Bug: 37973765
Change-Id: Ic8571c08dd92386d0e4f79d7866aeb0f19f38106
1 file changed