Add override_android_test.

This change also adds instrumentation_target_package to android_test, so
that the target package name in a test manifest can be easily
overridden.

Fixes: 134624457
Test: app_test.go
Change-Id: Ib8dd703da0038ac76210c92d79e133e37c718122

android/override_module.go

@@ -175,6 +175,7 @@ func RegisterOverridePostDepsMutators(ctx RegisterMutatorsContext) {
 	ctx.TopDown("register_override", registerOverrideMutator).Parallel()
 	ctx.BottomUp("perform_override", performOverrideMutator).Parallel()
 	ctx.BottomUp("overridable_deps", overridableModuleDepsMutator).Parallel()
+	ctx.BottomUp("replace_deps_on_override", replaceDepsOnOverridingModuleMutator).Parallel()
 }
 
 type overrideBaseDependencyTag struct {
@@ -218,6 +219,9 @@ func performOverrideMutator(ctx BottomUpMutatorContext) {
 			variants[i+1] = o.(Module).Name()
 		}
 		mods := ctx.CreateLocalVariations(variants...)
+		// Make the original variation the default one to depend on if no other override module variant
+		// is specified.
+		ctx.AliasVariation(variants[0])
 		for i, o := range overrides {
 			mods[i+1].(OverridableModule).override(ctx, o)
 		}
@@ -226,10 +230,18 @@ func performOverrideMutator(ctx BottomUpMutatorContext) {
 		// variant name rule for overridden modules, and thus allows ReplaceDependencies to match the
 		// two.
 		ctx.CreateLocalVariations(o.Name())
+		// To allow dependencies to be added without having to know the above variation.
+		ctx.AliasVariation(o.Name())
 	}
 }
 
 func overridableModuleDepsMutator(ctx BottomUpMutatorContext) {
+	if b, ok := ctx.Module().(OverridableModule); ok {
+		b.OverridablePropertiesDepsMutator(ctx)
+	}
+}
+
+func replaceDepsOnOverridingModuleMutator(ctx BottomUpMutatorContext) {
 	if b, ok := ctx.Module().(OverridableModule); ok {
 		if o := b.getOverriddenBy(); o != "" {
 			// Redirect dependencies on the overriding module to this overridden module. Overriding
@@ -237,6 +249,5 @@ func overridableModuleDepsMutator(ctx BottomUpMutatorContext) {
 			// modules. Therefore, dependencies on overriding modules need to be forwarded there as well.
 			ctx.ReplaceDependencies(o)
 		}
-		b.OverridablePropertiesDepsMutator(ctx)
 	}
 }