Add DynamicPartitionControlInterface::UpdateUsesSnapshotCompression

This function returns whether Virtual A/B
compression is enabled for the ongoing update.

Test: TH
Bug: 178732971
Change-Id: I781802443afd1d8deac046a8da198658220f7ba0
diff --git a/common/dynamic_partition_control_stub.h b/common/dynamic_partition_control_stub.h
index 0f428ab..822fa1b 100644
--- a/common/dynamic_partition_control_stub.h
+++ b/common/dynamic_partition_control_stub.h
@@ -70,6 +70,7 @@
   bool UnmapAllPartitions() override;
 
   bool IsDynamicPartition(const std::string& part_name) override;
+  bool UpdateUsesSnapshotCompression() override;
 };
 }  // namespace chromeos_update_engine