Add protobuf build test

Since we are the only ones using protobuf JS
this adds a test proto file to the public
repo so our build doesn't get broken by
accident.

BUG=1087037

Change-Id: I349c80e98d1b9e9d9cd414a418852eb2f899a7f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2254523
Auto-Submit: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780445}

chrome/browser/media/kaleidoscope/test/proto/BUILD.gn

+# Copyright 2020 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//third_party/closure_compiler/compile_js.gni")
+import("//third_party/protobuf/proto_library.gni")
+
+proto_library("proto") {
+  sources = [ "test.proto" ]
+
+  generate_javascript = true
+}
+
+js_library("test") {
+  sources = []
+
+  deps = [ ":proto_js" ]
+}

chrome/browser/media/kaleidoscope/test/proto/test.proto

+syntax = "proto3";
+
+message Test {
+  string id = 1;
+}

chrome/test/BUILD.gn

@@ -3657,6 +3657,7 @@ test("unit_tests") {
   }
 
   data_deps = [
+    "//chrome/browser/media/kaleidoscope/test/proto:test",
     "//chrome/test/data/media/engagement/preload:generate_preload_list",
     "//chrome/test/data/media/engagement/preload:test_data",
     "//testing/buildbot/filters:unit_tests_filters",