DynamicPartitionsControl: Add Virtual A/B feature flag.

Test: unittest
Bug: 138816109
Change-Id: I7ae65ba0bf36a6ca5085bc4ec2c46245288b4703
diff --git a/mock_dynamic_partition_control.h b/mock_dynamic_partition_control.h
index 26fc246..aab3c4d 100644
--- a/mock_dynamic_partition_control.h
+++ b/mock_dynamic_partition_control.h
@@ -49,6 +49,7 @@
                     uint32_t,
                     const BootControlInterface::PartitionMetadata&));
   MOCK_METHOD1(GetSuperPartitionName, std::string(uint32_t));
+  MOCK_METHOD0(GetVirtualAbFeatureFlag, FeatureFlag());
 };
 
 class MockDynamicPartitionControlAndroid
@@ -75,6 +76,7 @@
   MOCK_METHOD1(GetDeviceDir, bool(std::string*));
   MOCK_METHOD0(GetDynamicPartitionsFeatureFlag, FeatureFlag());
   MOCK_METHOD1(GetSuperPartitionName, std::string(uint32_t));
+  MOCK_METHOD0(GetVirtualAbFeatureFlag, FeatureFlag());
 };
 
 }  // namespace chromeos_update_engine