Add support for java_defaults modules

Test: java_test.go
Change-Id: I6dba1671c7eb019183af94bb7b10810296740101
diff --git a/android/defaults.go b/android/defaults.go
index 3ec3ff4..4bf872e 100644
--- a/android/defaults.go
+++ b/android/defaults.go
@@ -117,7 +117,7 @@
 	}
 }
 
-func registerDefaultsPreArchMutators(ctx RegisterMutatorsContext) {
+func RegisterDefaultsPreArchMutators(ctx RegisterMutatorsContext) {
 	ctx.BottomUp("defaults_deps", defaultsDepsMutator).Parallel()
 	ctx.TopDown("defaults", defaultsMutator).Parallel()
 }
diff --git a/android/mutator.go b/android/mutator.go
index 86a5b85..c8f3e8f 100644
--- a/android/mutator.go
+++ b/android/mutator.go
@@ -75,7 +75,7 @@
 		ctx.TopDown("load_hooks", loadHookMutator).Parallel()
 	},
 	registerPrebuiltsPreArchMutators,
-	registerDefaultsPreArchMutators,
+	RegisterDefaultsPreArchMutators,
 }
 
 var preDeps = []RegisterMutatorFunc{