[Chromecast] Fix unit test failures due to underflow.

chromecast/media/cma/backend/alsa/stream_mixer_alsa_input_impl.cc

Index: chromecast/media/cma/backend/alsa/stream_mixer_alsa_input_impl.cc
diff --git a/chromecast/media/cma/backend/alsa/stream_mixer_alsa_input_impl.cc b/chromecast/media/cma/backend/alsa/stream_mixer_alsa_input_impl.cc
index 6df49ef5e834d9f46b19ac4852b875559fd53506..656130bed534469bea6c3c3510c2195860853d9d 100644
--- a/chromecast/media/cma/backend/alsa/stream_mixer_alsa_input_impl.cc
+++ b/chromecast/media/cma/backend/alsa/stream_mixer_alsa_input_impl.cc
@@ -208,6 +208,10 @@ MediaPipelineBackendAlsa::RenderingDelay StreamMixerAlsaInputImpl::QueueData(
     queued_frames_including_resampler_ += frames;
   }
 
+  if (is_underflowing_) {
+    return MediaPipelineBackendAlsa::RenderingDelay();
+  }
+
   MediaPipelineBackendAlsa::RenderingDelay delay = mixer_rendering_delay_;
   if (delay.timestamp_microseconds != kNoTimestamp) {
     delay.delay_microseconds += static_cast<int64_t>(