Move enable_webrtc to a buildflag header.

remoting/host/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("//build/util/process_version.gni")
+import("//media/media_options.gni")
 import("//remoting/build/config/remoting_build.gni")
 
 group("all_tests") {
   testonly = true
 
   deps = [
     ":unit_tests",
   ]
 }
 
@@ skipping 828 matching lines @@
     group("remoting_me2me_host_archive") {
       deps = [
         "//remoting/host/installer/mac:remoting_me2me_host_archive",
       ]
     }
   } else {
     group("remoting_me2me_host_archive") {
     }
   }
 }