Allow forward merge on powerwash.

If package schedules powerwash, snapshots on a Virtual A/B device
will be deleted. Tell SnapshotManager to handle this case.

Test: apply downgrade package
Test: apply package with wipe
Test: apply package then manually wipe
Bug: 152094219
Change-Id: I8601b661924abcc82956788e2f33cdb70d71f778
diff --git a/common/dynamic_partition_control_interface.h b/common/dynamic_partition_control_interface.h
index d5db9bc..58ebfe4 100644
--- a/common/dynamic_partition_control_interface.h
+++ b/common/dynamic_partition_control_interface.h
@@ -87,7 +87,7 @@
 
   // After writing to new partitions, before rebooting into the new slot, call
   // this function to indicate writes to new partitions are done.
-  virtual bool FinishUpdate() = 0;
+  virtual bool FinishUpdate(bool powerwash_required) = 0;
 
   // Get an action to clean up previous update.
   // Return NoOpAction on non-Virtual A/B devices.