Define remote playback proto buffer

media/media_options.gni

Index: media/media_options.gni
diff --git a/media/media_options.gni b/media/media_options.gni
index 424d85658adf64fc15e94b2ef142eb19e13d26aa..259b0ec782a3a318225ba51ee862050d1613fa64 100644
--- a/media/media_options.gni
+++ b/media/media_options.gni
@@ -123,3 +123,8 @@ declare_args() {
     }
   }
 }
+
+declare_args() {
+  # flag to enable media remoting feature.
+  media_remoting = true
+}