Convert USE_PROPRIETARY_CODECS to a buildflag header.

extensions/browser/api/display_source/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.
 
 import("//build/config/features.gni")
 import("//extensions/features/features.gni")
+import("//media/media_options.gni")
 
 source_set("display_source") {
   sources = [
     "display_source_api.cc",
     "display_source_api.h",
     "display_source_connection_delegate.cc",
     "display_source_connection_delegate.h",
     "display_source_connection_delegate_factory.cc",
     "display_source_connection_delegate_factory.h",
     "display_source_event_router.cc",
@@ skipping 10 matching lines @@
         "wifi_display/wifi_display_session_service_impl.cc",
         "wifi_display/wifi_display_session_service_impl.h",
       ]
     }
   }
 
   deps = [
     "//extensions/common/api",
   ]
 }