Fix S and T mixed build OTA

When a device has vendor partitions in S and system partitions in T, ota
package will enable VABC XOR. But device's snapuserd actually doesn't
support XOR, because snapuserd is in vendor partition. Therefore, at
runtime, check if XOR is supported.

Test: th
Bug: 227614163

Change-Id: I4cb84aa9b69ff872f5de7a5e9c5ca1e3405d2d8b
diff --git a/common/dynamic_partition_control_stub.h b/common/dynamic_partition_control_stub.h
index 5aa4336..15137d2 100644
--- a/common/dynamic_partition_control_stub.h
+++ b/common/dynamic_partition_control_stub.h
@@ -27,11 +27,12 @@
 
 namespace chromeos_update_engine {
 
-class DynamicPartitionControlStub : public DynamicPartitionControlInterface {
+class DynamicPartitionControlStub final : public DynamicPartitionControlInterface {
  public:
   FeatureFlag GetDynamicPartitionsFeatureFlag() override;
   FeatureFlag GetVirtualAbFeatureFlag() override;
   FeatureFlag GetVirtualAbCompressionFeatureFlag() override;
+  FeatureFlag GetVirtualAbCompressionXorFeatureFlag() override;
   bool OptimizeOperation(const std::string& partition_name,
                          const InstallOperation& operation,
                          InstallOperation* optimized) override;