[Chromoting] Add DataChannelManager to manage optional incoming data channels

remoting/proto/BUILD.gn

 # Copyright 2014 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/protobuf/proto_library.gni")
 
 group("proto_lite") {
   public_deps = [
     ":proto",
     "//third_party/protobuf:protobuf_lite",
   ]
 }
 
 proto_library("proto") {
   sources = [
     "audio.proto",
     "control.proto",
     "event.proto",
     "internal.proto",
     "mux.proto",
     "process_stats.proto",
+    "test.proto",
     "video.proto",
     "video_stats.proto",
   ]
 }