Micro change suggested by internal style tool.

webrtc/modules/audio_mixer/frame_combiner.cc

Index: webrtc/modules/audio_mixer/frame_combiner.cc
diff --git a/webrtc/modules/audio_mixer/frame_combiner.cc b/webrtc/modules/audio_mixer/frame_combiner.cc
index 4e4fd5662263d569773154df53c1fc3ad5ecb62b..d08ed0f4739ba77b0fe0f5ab4dc4f8cc12fed397 100644
--- a/webrtc/modules/audio_mixer/frame_combiner.cc
+++ b/webrtc/modules/audio_mixer/frame_combiner.cc
@@ -97,7 +97,7 @@ void FrameCombiner::Combine(const std::vector<AudioFrame*>& mix_list,
       -1, 0, nullptr, samples_per_channel, sample_rate, AudioFrame::kUndefined,
       AudioFrame::kVadUnknown, number_of_channels);
 
-  if (mix_list.size() == 0) {
+  if (mix_list.empty()) {
     CombineZeroFrames(audio_frame_for_mixing);
   } else if (mix_list.size() == 1) {
     CombineOneFrame(mix_list.front(), audio_frame_for_mixing);