Add unit test for fallback route of manifest cache

Test: Run atest
Change-Id: Icc6a2c809c571c3ad8e16a863c37afd8d4042ed6
diff --git a/Android.bp b/Android.bp
index ecf3585..4e3e248 100644
--- a/Android.bp
+++ b/Android.bp
@@ -671,6 +671,7 @@
         "payload_consumer/certificate_parser_android_unittest.cc",
         "payload_consumer/delta_performer_integration_test.cc",
         "payload_consumer/delta_performer_unittest.cc",
+        "payload_consumer/download_action_android_unittest.cc",
         "payload_consumer/extent_reader_unittest.cc",
         "payload_consumer/extent_writer_unittest.cc",
         "payload_consumer/fake_file_descriptor.cc",