Moved injection of AudioDecoderFactory into voe::Channel.

Channel's API remains unchanged, but the creation of a BuiltinAudioDecoderFactory is now in Channel. The next step would be to amend Channel's API (through CreateChannel, I believe) to allow an AudioDecoderFactory to be sent along.

BUG=webrtc:5805

Review-Url: https://codereview.webrtc.org/1992763002
Cr-Commit-Position: refs/heads/master@{#12893}

webrtc/modules/audio_coding/neteq/tools/neteq_rtpplay.cc

@@ -26,6 +26,7 @@
 #include "gflags/gflags.h"
 #include "webrtc/base/checks.h"
 #include "webrtc/base/safe_conversions.h"
+#include "webrtc/modules/audio_coding/codecs/builtin_audio_decoder_factory.h"
 #include "webrtc/modules/audio_coding/codecs/pcm16b/pcm16b.h"
 #include "webrtc/modules/audio_coding/neteq/include/neteq.h"
 #include "webrtc/modules/audio_coding/neteq/tools/input_audio_file.h"
@@ -474,7 +475,8 @@ int main(int argc, char* argv[]) {
   // Initialize NetEq instance.
   NetEq::Config config;
   config.sample_rate_hz = sample_rate_hz;
-  NetEq* neteq = NetEq::Create(config);
+  NetEq* neteq =
+      NetEq::Create(config, CreateBuiltinAudioDecoderFactory());
   RegisterPayloadTypes(neteq);