Enable injection of a custom NetEqFactory into PeerConnectionFactory.

Injecting both a custom NetEqFactory and an AudioDecoderFactory is not
supported, in that case the AudioDecoderFactory should be wrapped inside
the NetEqFactory.

Bug: webrtc:11005
Change-Id: I4e311eb1bfa03c91bca587d70540e81829f881c9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/158720
Commit-Queue: Ivo Creusen <ivoc@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29673}
diff --git a/pc/peer_connection_factory.h b/pc/peer_connection_factory.h
index 648a3af..5886dee 100644
--- a/pc/peer_connection_factory.h
+++ b/pc/peer_connection_factory.h
@@ -127,6 +127,7 @@
   std::unique_ptr<NetworkControllerFactoryInterface>
       injected_network_controller_factory_;
   std::unique_ptr<MediaTransportFactory> media_transport_factory_;
+  std::unique_ptr<NetEqFactory> neteq_factory_;
 };
 
 }  // namespace webrtc