Audio codec implementations: Take optional codec ID argument

None of the built-in codecs do anything with the ID, but callers will
soon require them to accept it.

Bug: webrtc:8941
Change-Id: I0eb77db82d72c7d34cff639fecb67c1e6ec421bf
Reviewed-on: https://webrtc-review.googlesource.com/58089
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22259}

api/audio_codecs/ilbc/audio_decoder_ilbc.cc

@@ -33,7 +33,8 @@ void AudioDecoderIlbc::AppendSupportedDecoders(
 }
 
 std::unique_ptr<AudioDecoder> AudioDecoderIlbc::MakeAudioDecoder(
-    Config config) {
+    Config config,
+    rtc::Optional<AudioCodecPairId> /*codec_pair_id*/) {
   return rtc::MakeUnique<AudioDecoderIlbcImpl>();
 }