[Chromecast] Fix small mixer bugs

 * Make it so the old command-line arg to set a fixed output sample rate
   works.
 * Avoid NaN in postprocessor volume calculation.

Bug: internal b/74089224
Change-Id: Ic9534d16e8eff5e24faf3cac8b41e8aa63c3397a
Reviewed-on: https://chromium-review.googlesource.com/960966Reviewed-by: Stephen Lanham <slan@chromium.org>
Commit-Queue: Kenneth MacKay <kmackay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542975}

chromecast/media/cma/backend/post_processing_pipeline_impl.cc

@@ -192,7 +192,7 @@ void PostProcessingPipelineImpl::UpdateCastVolume(float multiplier) {
     return;
   }
   current_multiplier_ = multiplier;
-  current_dbfs_ = std::log10(multiplier) * 20;
+  current_dbfs_ = (multiplier == 0.0f ? -200.0f : std::log10(multiplier) * 20);
   DCHECK(chromecast::media::VolumeControl::DbFSToVolume);
   cast_volume_ = chromecast::media::VolumeControl::DbFSToVolume(current_dbfs_);
 }

chromecast/media/cma/backend/stream_mixer.cc

@@ -86,13 +86,11 @@ int GetFixedSampleRate() {
   int fixed_sample_rate = GetSwitchValueNonNegativeInt(
       switches::kAudioOutputSampleRate, MixerOutputStream::kInvalidSampleRate);
 
-#if defined(USE_ALSA)
   if (fixed_sample_rate == MixerOutputStream::kInvalidSampleRate) {
     fixed_sample_rate =
         GetSwitchValueNonNegativeInt(switches::kAlsaFixedOutputSampleRate,
                                      MixerOutputStream::kInvalidSampleRate);
   }
-#endif  // defined(USE_ALSA)
   return fixed_sample_rate;
 }