Call SnapshotManager::FinishedSnapshotWrites

... when the update has finished. This allows SnapshotManager
to conclude the update and prepare for reboot.

Test: builds
Test: apply OTA on Virtual A/B device, then check
/metadata/ota/snapshot-boot exists, then reboot
Bug: 138816109
Change-Id: I2a4699865b09358ef018313bed64e34617a78e3c
diff --git a/dynamic_partition_control_android.h b/dynamic_partition_control_android.h
index 9509a62..f9dfd89 100644
--- a/dynamic_partition_control_android.h
+++ b/dynamic_partition_control_android.h
@@ -52,6 +52,7 @@
       const DeltaArchiveManifest& manifest) override;
   bool GetDeviceDir(std::string* path) override;
   std::string GetSuperPartitionName(uint32_t slot) override;
+  bool FinishUpdate() override;
 
  protected:
   // These functions are exposed for testing.