Added some TestApi that are already used by CTS

Allows us to remove the use of private platform API from CTS.

Bug: 124134247
Test: builds
Change-Id: Iceb81ff7c9385e877d2612fbb7b506245d116928
diff --git a/proto/Android.bp b/proto/Android.bp
index 817a54d..7f826b3 100644
--- a/proto/Android.bp
+++ b/proto/Android.bp
@@ -6,6 +6,7 @@
     },
     srcs: ["src/**/*.proto"],
     no_framework_libs: true,
+    sdk_version: "9",
     // Pin java_version until jarjar is certified to support later versions. http://b/72703434
     java_version: "1.8",
     target: {