Fix channel layout config for multi-channel Opus encoded audio

Test: Played 5.1 opus encoded audio file through chromecast by pointing the chromecast to a local server and audio comes out of the AVR at the expected channel.
Bug: b/133189747
Change-Id: Ia0e77ea9f6f8b3f9cd35803dffa5888fec0335d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627759Reviewed-by: Sergey Volk <servolk@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Sergey Volk <servolk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664079}

chromecast/media/cma/backend/audio_decoder_software_wrapper.cc

@@ -113,6 +113,7 @@ bool AudioDecoderSoftwareWrapper::SetConfig(const AudioConfig& config) {
   output_config_.bytes_per_channel = 2;
   output_config_.samples_per_second = config.samples_per_second;
   output_config_.encryption_scheme = EncryptionScheme::kUnencrypted;
+  output_config_.channel_layout = config.channel_layout;
   return backend_decoder_->SetConfig(output_config_);
 }
 

chromecast/media/cma/base/decoder_config_adapter.cc

@@ -55,6 +55,7 @@ ChannelLayout ToChannelLayout(const ::media::ChannelLayout channel_layout) {
     case ::media::ChannelLayout::CHANNEL_LAYOUT_STEREO:
       return ChannelLayout::STEREO;
     case ::media::ChannelLayout::CHANNEL_LAYOUT_5_1:
+    case ::media::ChannelLayout::CHANNEL_LAYOUT_5_1_BACK:
       return ChannelLayout::SURROUND_5_1;
     case ::media::ChannelLayout::CHANNEL_LAYOUT_BITSTREAM:
       return ChannelLayout::BITSTREAM;