Move enable_webrtc to a buildflag header.

content/public/renderer/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("//ppapi/features/features.gni")
 
 # See //content/BUILD.gn for how this works.
 group("renderer") {
   if (is_component_build) {
     public_deps = [
       "//content",
     ]
   } else {
     public_deps = [
@@ skipping 94 matching lines @@
     deps += [
       "//content/public/common:feature_h264_with_openh264_ffmpeg",
       "//content/public/common:features",
     ]
   }
 
   if (enable_plugins) {
     sources += [ "plugin_instance_throttler.h" ]
   }
 }