Revert of Media Router GYP/GN cleanup

chrome/browser/extensions/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/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 
 assert(enable_extensions)
 
@@ skipping 184 matching lines @@
                     ".",
                     "//chrome")
   }
 
   if (is_chromeos && use_ozone) {
     sources -= [ "global_shortcut_listener_chromeos.cc" ]
   }
   if (!use_ozone) {
     sources -= [ "global_shortcut_listener_ozone.cc" ]
   }
+  if (enable_media_router) {
+    defines += [ "ENABLE_MEDIA_ROUTER=1" ]
+  }
 }