Move enable_webrtc to a buildflag header.

remoting/host/it2me/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/config/features.gni")
+import("//media/media_options.gni")
 import("//remoting/remoting_enable.gni")
 import("//remoting/remoting_locales.gni")
 import("//remoting/remoting_version.gni")
 
 if (is_win) {
   import("//remoting/host/predefines_win.gni")
 }
 if (is_mac) {
   import("//build/config/mac/rules.gni")
   import("//third_party/icu/config.gni")
@@ skipping 219 matching lines @@
       if (is_desktop_linux) {
         if (use_gtk3) {
           deps += [ "//build/config/linux/gtk3" ]
         } else {
           deps += [ "//build/config/linux/gtk2" ]
         }
       }
     }
   }
 }