Refactor NetEqTestFactory to not use "external" decoders

Bug: webrtc:10080
Change-Id: Icfca98d6d91fc5139e678c1aa3de1e2c35abff5c
Reviewed-on: https://webrtc-review.googlesource.com/c/115240
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26090}
diff --git a/modules/audio_coding/BUILD.gn b/modules/audio_coding/BUILD.gn
index 6583376..7b50c19 100644
--- a/modules/audio_coding/BUILD.gn
+++ b/modules/audio_coding/BUILD.gn
@@ -1492,6 +1492,7 @@
         "../..:webrtc_common",
         "../../api/audio_codecs:builtin_audio_decoder_factory",
         "../../rtc_base:rtc_base_approved",
+        "../../test:audio_codec_mocks",
         "../../test:test_support",
         "//third_party/abseil-cpp/absl/memory",
       ]