Cast: IPC glue between cast library transport and encoders.

media/cast/cast_sender.gyp

Index: media/cast/cast_sender.gyp
diff --git a/media/cast/cast_sender.gyp b/media/cast/cast_sender.gyp
index 7b4def6863fd8bd8c87c9d39cfcb5e5f6d7eb4b4..831c257ca64ebd3c0f93004c7f0f5f37a474f7bc 100644
--- a/media/cast/cast_sender.gyp
+++ b/media/cast/cast_sender.gyp
@@ -28,6 +28,9 @@
         'rtcp/rtcp.gyp:cast_rtcp',
         'video_sender',
       ], # dependencies
+      'defines' : [
+        'MEDIA_IMPLEMENTATION',
+      ],
     },
   ],
 }