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/video/BUILD.gn b/video/BUILD.gn
index 3d2d5e9..1ec0e6a 100644
--- a/video/BUILD.gn
+++ b/video/BUILD.gn
@@ -56,6 +56,7 @@
   deps = [
     "..:webrtc_common",
     "../:typedefs",
+    "../api:fec_controller_api",
     "../api:libjingle_peerconnection_api",
     "../api:optional",
     "../api:transport_api",