Audio codec factories: Pass a codec pair ID to new codecs

Currently ignored by all implementations and callers, but future CLs
will remedy that.

Bug: webrtc:8941
Change-Id: I59a3af78fefcf35af3e5ef37d2adf1165ce5751e
Reviewed-on: https://webrtc-review.googlesource.com/58080
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22248}
diff --git a/api/audio_codecs/BUILD.gn b/api/audio_codecs/BUILD.gn
index f730260..fb033f2 100644
--- a/api/audio_codecs/BUILD.gn
+++ b/api/audio_codecs/BUILD.gn
@@ -15,12 +15,16 @@
 rtc_source_set("audio_codecs_api") {
   visibility = [ "*" ]
   sources = [
+    "audio_codec_pair_id.cc",
+    "audio_codec_pair_id.h",
     "audio_decoder.cc",
     "audio_decoder.h",
+    "audio_decoder_factory.cc",
     "audio_decoder_factory.h",
     "audio_decoder_factory_template.h",
     "audio_encoder.cc",
     "audio_encoder.h",
+    "audio_encoder_factory.cc",
     "audio_encoder_factory.h",
     "audio_encoder_factory_template.h",
     "audio_format.cc",