Add thread accessors to Call.

Classes associated with the Call instance, need access to these threads
and/or awareness, for checking for thread correctness.

Bug: webrtc:11993
Change-Id: I93bcee0657875f211be2ec959b96f818fa9fd8a0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215584
Reviewed-by: Markus Handell <handellm@webrtc.org>
Commit-Queue: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33772}
diff --git a/call/degraded_call.h b/call/degraded_call.h
index d81c65c..03fc14f 100644
--- a/call/degraded_call.h
+++ b/call/degraded_call.h
@@ -87,6 +87,9 @@
 
   const WebRtcKeyValueConfig& trials() const override;
 
+  TaskQueueBase* network_thread() const override;
+  TaskQueueBase* worker_thread() const override;
+
   void SignalChannelNetworkState(MediaType media, NetworkState state) override;
   void OnAudioTransportOverheadChanged(
       int transport_overhead_per_packet) override;