DynamicPartitionsControl: Add Virtual A/B feature flag.

Test: unittest
Bug: 138816109
Change-Id: I7ae65ba0bf36a6ca5085bc4ec2c46245288b4703
diff --git a/dynamic_partition_control_android.cc b/dynamic_partition_control_android.cc
index 5a2ccb1..b973232 100644
--- a/dynamic_partition_control_android.cc
+++ b/dynamic_partition_control_android.cc
@@ -53,6 +53,8 @@
 constexpr char kUseDynamicPartitions[] = "ro.boot.dynamic_partitions";
 constexpr char kRetrfoitDynamicPartitions[] =
     "ro.boot.dynamic_partitions_retrofit";
+constexpr char kVirtualAbEnabled[] = "ro.virtual_ab.enabled";
+constexpr char kVirtualAbRetrofit[] = "ro.virtual_ab.retrofit";
 constexpr uint64_t kMapTimeoutMillis = 1000;
 
 DynamicPartitionControlAndroid::~DynamicPartitionControlAndroid() {
@@ -81,6 +83,10 @@
   return GetFeatureFlag(kUseDynamicPartitions, kRetrfoitDynamicPartitions);
 }
 
+FeatureFlag DynamicPartitionControlAndroid::GetVirtualAbFeatureFlag() {
+  return GetFeatureFlag(kVirtualAbEnabled, kVirtualAbRetrofit);
+}
+
 bool DynamicPartitionControlAndroid::MapPartitionInternal(
     const std::string& super_device,
     const std::string& target_partition_name,