[Chromecast] Fix unit test failures due to underflow.

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chromecast/media/cma/backend/alsa/stream_mixer_alsa_input_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/bind.h"
@@ skipping 190 matching lines @@
 MediaPipelineBackendAlsa::RenderingDelay StreamMixerAlsaInputImpl::QueueData(
     const scoped_refptr<DecoderBufferBase>& data) {
   queue_lock_.AssertAcquired();
   if (!data->end_of_stream()) {
     int frames = data->data_size() / (kNumOutputChannels * sizeof(float));
     queue_.push_back(data);
     queued_frames_ += frames;
     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>(
         queued_frames_including_resampler_ *
         base::Time::kMicrosecondsPerSecond / input_samples_per_second_);
   }
   return delay;
 }
 
 void StreamMixerAlsaInputImpl::PostPcmCallback(
@@ skipping 301 matching lines @@
 
 void StreamMixerAlsaInputImpl::VolumeScaleAccumulate(bool repeat_transition,
                                                      const float* src,
                                                      int frames,
                                                      float* dest) {
   slew_volume_.ProcessFMAC(repeat_transition, src, frames, dest);
 }
 
 }  // namespace media
 }  // namespace chromecast