Implement OutputFileProducer for android_app_import and android_test_import

Fixes: 290376750
Test: builds
Change-Id: I5fc3a759462cfd4342b9330ac8978368feee26ca
diff --git a/java/app_import.go b/java/app_import.go
index 9c01960..8427217 100644
--- a/java/app_import.go
+++ b/java/app_import.go
@@ -17,6 +17,7 @@
 // This file contains the module implementations for android_app_import and android_test_import.
 
 import (
+	"fmt"
 	"reflect"
 
 	"github.com/google/blueprint"
@@ -410,6 +411,15 @@
 	return a.outputFile
 }
 
+func (a *AndroidAppImport) OutputFiles(tag string) (android.Paths, error) {
+	switch tag {
+	case "":
+		return []android.Path{a.outputFile}, nil
+	default:
+		return nil, fmt.Errorf("unsupported module reference tag %q", tag)
+	}
+}
+
 func (a *AndroidAppImport) JacocoReportClassesFile() android.Path {
 	return nil
 }