Add monostate to optional safe unions.

Bug: 116156870
Test: hidl_test, hidl_test_java
Change-Id: Ie17a80dee982775e267a39086016071ac2361fb5
diff --git a/tests/safeunion/1.0/Android.bp b/tests/safeunion/1.0/Android.bp
index ede8401..87edd53 100644
--- a/tests/safeunion/1.0/Android.bp
+++ b/tests/safeunion/1.0/Android.bp
@@ -9,6 +9,7 @@
     ],
     interfaces: [
         "android.hidl.base@1.0",
+        "android.hidl.safe_union@1.0",
     ],
     gen_java: true,
 }