add apex_defaults

apex_defaults is the default module for apex.

Bug: 124026431
Test: m (apex_test updated)
Change-Id: I09f63046e909e8eeb52ecec6bb07eb51e5490561
diff --git a/apex/apex.go b/apex/apex.go
index 06e6c78..092868e 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -137,6 +137,7 @@
 	pctx.HostBinToolVariable("zipalign", "zipalign")
 
 	android.RegisterModuleType("apex", ApexBundleFactory)
+	android.RegisterModuleType("apex_defaults", defaultsFactory)
 
 	android.PostDepsMutators(func(ctx android.RegisterMutatorsContext) {
 		ctx.TopDown("apex_deps", apexDepsMutator)
@@ -1103,3 +1104,31 @@
 	android.InitDefaultableModule(module)
 	return module
 }
+
+//
+// Defaults
+//
+type Defaults struct {
+	android.ModuleBase
+	android.DefaultsModuleBase
+}
+
+func (*Defaults) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+}
+
+func defaultsFactory() android.Module {
+	return DefaultsFactory()
+}
+
+func DefaultsFactory(props ...interface{}) android.Module {
+	module := &Defaults{}
+
+	module.AddProperties(props...)
+	module.AddProperties(
+		&apexBundleProperties{},
+		&apexTargetBundleProperties{},
+	)
+
+	android.InitDefaultsModule(module)
+	return module
+}