Make fec controller plug-able.

Bug: webrtc:8656
Change-Id: I3d42ffc92a7c95266e5d53bab03f388bd0de2592
Reviewed-on: https://webrtc-review.googlesource.com/39760
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Ying Wang <yinwa@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21710}
diff --git a/modules/video_coding/include/video_coding.h b/modules/video_coding/include/video_coding.h
index d204f19..5173710 100644
--- a/modules/video_coding/include/video_coding.h
+++ b/modules/video_coding/include/video_coding.h
@@ -21,6 +21,7 @@
 #include <windows.h>
 #endif
 
+#include "api/fec_controller.h"
 #include "api/video/video_frame.h"
 #include "modules/include/module.h"
 #include "modules/include/module_common_types.h"