[AppRemoting] Break out AppRemoting shared module (re-land).

remoting/remoting_options.gni

 # Copyright 2015 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.
 
 # These arguments can be overridden from the command line (see "gn help args").
 declare_args() {
   # Set this to run the jscompile checks after building the webapp.
   enable_remoting_jscompile = false
 }
 
 # Set this to enable cast mode on the android client.
 enable_cast = 0
 
+# Set this to enable building internal AppRemoting apps.
+enable_internal_app_remoting_targets = false
+
 # Set this to use GCD instead of the remoting directory service.
 remoting_use_gcd = 0
 
 # Enable the multi-process host on Windows by default.
 if (is_win) {
   remoting_multi_process = 1
 } else {
   remoting_multi_process = 0
 }
 
 remoting_rdp_session = 1
 
 branding_path = "../remoting/branding_<(branding)"
 
 # The ar_service_environment variable is used to define the target
 # environment for the app being built.
 # The allowed values are dev, test, staging, prod, and prod-testing.
 if (is_debug) {
   ar_service_environment = "dev"
 } else {
   # Non-dev builds should default to 'prod'.
   ar_service_environment = "prod"
 }