Add java_aconfig_library for Media BeTo host tests

Bug: 319604746
Change-Id: Ia9fd17248d9541bddb5a8989ae77aeff55592470
Test: Used in ag/25902228.
diff --git a/AconfigFlags.bp b/AconfigFlags.bp
index 0916227..2ae72ef 100644
--- a/AconfigFlags.bp
+++ b/AconfigFlags.bp
@@ -456,6 +456,13 @@
     defaults: ["framework-minus-apex-aconfig-java-defaults"],
 }
 
+java_aconfig_library {
+    name: "com.android.media.flags.bettertogether-aconfig-java-host",
+    aconfig_declarations: "com.android.media.flags.bettertogether-aconfig",
+    host_supported: true,
+    defaults: ["framework-minus-apex-aconfig-java-defaults"],
+}
+
 // Media TV
 aconfig_declarations {
     name: "android.media.tv.flags-aconfig",