Add dexpreopt enabled tests

Add tests that verify when dexpreopt is enabled or disabled.

Test: dexpreopt_test.go
Change-Id: Ideba9c0dac30eb31e7ae29e46d1d1590202b8369
diff --git a/Android.bp b/Android.bp
index 37be36c..29ad569 100644
--- a/Android.bp
+++ b/Android.bp
@@ -255,6 +255,7 @@
     ],
     testSrcs: [
         "java/app_test.go",
+        "java/dexpreopt_test.go",
         "java/java_test.go",
         "java/jdeps_test.go",
     ],