Media Remoting: Add RemotingController.

media/media_options.gni

Index: media/media_options.gni
diff --git a/media/media_options.gni b/media/media_options.gni
index d6ab4f4249fdf03b06e294cc4f537fe282e66ab1..c412b25a91910e42378ce0bc98dd6df404a0cb7c 100644
--- a/media/media_options.gni
+++ b/media/media_options.gni
@@ -119,3 +119,8 @@ declare_args() {
     }
   }
 }
+
+declare_args() {
+  # Enable to switch media renderer between remoting and local playback.

[xhwang, 2016/10/05 17:36:41]

Could you please explain more about what "remoting" is? Also, you are not
"switching" one media renderer between remoting and local playback, you are
switching between local renderer and remoting renderer...

[miu, 2016/10/05 19:13:57]

Also, it would be more accurate to say that this switch defines whether the
Media Remoting implementation will be built.

[xjz, 2016/10/05 23:39:02]

Done.

[xjz, 2016/10/05 23:39:02]

Done.

+  enable_media_remoting = !is_chromecast && !is_ios && !is_android
+}