Move enable_webrtc to a buildflag header.

media/gpu/ipc/service/BUILD.gn

 # Copyright 2016 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.
 
 if (is_component_build) {
   link_target_type = "source_set"
 } else {
   link_target_type = "static_library"
 }
 target(link_target_type, "service") {
@@ skipping 21 matching lines @@
 
   public_deps = [
     "//base",
     "//gpu/config",
     "//ipc",
     "//media",
     "//media/gpu",
   ]
   deps = [
     "//gpu/ipc/service",
+    "//media:media_features",
     "//media/gpu/ipc/common",
     "//third_party/mesa:mesa_headers",
     "//ui/gfx/ipc/color",
   ]
 
   configs += [ "//media/gpu:gpu_config" ]
 
   if (is_chromeos && current_cpu != "arm") {
     configs += [ "//third_party/libva:libva_config" ]
   }
 
   if (is_win) {
     configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
   }
 
   if (is_mac) {
     deps += [ "//third_party/webrtc/common_video:common_video" ]
   }
 }