Fix Gn untracked headers in webrtc/call.

This CL is the same CL we had at https://codereview.webrtc.org/3014543002/.
Since we cannot land it with Rietveld anymore let's move the discussion
to Gerrit.

BUG=webrtc:7641
CQ_INCLUDE_TRYBOTS=master.internal.tryserver.corp.webrtc:linux_internal

Change-Id: I5662bec318544b07f476c12ecada997d726e7361
Reviewed-on: https://webrtc-review.googlesource.com/7981
Reviewed-by: Henrik Kjellander <kjellander@google.com>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20224}
diff --git a/audio/BUILD.gn b/audio/BUILD.gn
index 6917713..a9ca0d5 100644
--- a/audio/BUILD.gn
+++ b/audio/BUILD.gn
@@ -40,6 +40,7 @@
     "../api:optional",
     "../api/audio_codecs:audio_codecs_api",
     "../api/audio_codecs:builtin_audio_encoder_factory",
+    "../call:bitrate_allocator",
     "../call:call_interfaces",
     "../call:rtp_interfaces",
     "../common_audio",