Add |native_bridge_experiment| to arc.proto

BUG=b:63133475
TEST=./build_packages

Change-Id: Ib358e569503e1f9fe096dbe97c964b30f920d15d
Reviewed-on: https://chromium-review.googlesource.com/615092
Commit-Ready: Lev Rumyantsev <levarum@chromium.org>
Tested-by: Lev Rumyantsev <levarum@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
1 file changed