Move enable_webrtc to a buildflag header.

jingle/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("//testing/test.gni")
 
 if (enable_webrtc || !is_android) {
   static_library("jingle_glue") {
     sources = [
       "glue/chrome_async_socket.cc",
       "glue/chrome_async_socket.h",
       "glue/fake_ssl_client_socket.cc",
       "glue/fake_ssl_client_socket.h",
       "glue/proxy_resolving_client_socket.cc",
@@ skipping 192 matching lines @@
     ]
     deps = [
       "//base",
       "//net",
     ]
   }
 
   source_set("notifier_test_util") {
   }
 }