Add support for .proto files in java modules

Test: m -j checkbuild
Change-Id: Ia03429948baebff85164a91a34507866c97a08ef
diff --git a/Android.bp b/Android.bp
index 0e57c12..ae31a60 100644
--- a/Android.bp
+++ b/Android.bp
@@ -209,6 +209,7 @@
         "java/builder.go",
         "java/gen.go",
         "java/java.go",
+        "java/proto.go",
         "java/resources.go",
     ],
     testSrcs: [