Adding BitrateController to audio network adaptor.

BUG=webrtc:6303

Review-Url: https://codereview.webrtc.org/2334613002
Cr-Commit-Position: refs/heads/master@{#14293}
diff --git a/webrtc/modules/audio_coding/BUILD.gn b/webrtc/modules/audio_coding/BUILD.gn
index b6e2db3..4fe49e5 100644
--- a/webrtc/modules/audio_coding/BUILD.gn
+++ b/webrtc/modules/audio_coding/BUILD.gn
@@ -699,6 +699,8 @@
     "audio_network_adaptor/audio_network_adaptor.cc",
     "audio_network_adaptor/audio_network_adaptor_impl.cc",
     "audio_network_adaptor/audio_network_adaptor_impl.h",
+    "audio_network_adaptor/bitrate_controller.cc",
+    "audio_network_adaptor/bitrate_controller.h",
     "audio_network_adaptor/channel_controller.cc",
     "audio_network_adaptor/channel_controller.h",
     "audio_network_adaptor/controller.cc",