Micro change suggested by internal style tool.

webrtc/modules/audio_mixer/frame_combiner.cc

 /*
  *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 79 matching lines @@
   }
 
   // TODO(aleloi): Issue bugs.webrtc.org/3390.
   // Audio frame timestamp. The 'timestamp_' field is set to dummy
   // value '0', because it is only supported in the one channel case and
   // is then updated in the helper functions.
   audio_frame_for_mixing->UpdateFrame(
       -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);
   } else {
     std::vector<rtc::ArrayView<const int16_t>> input_frames;
     for (size_t i = 0; i < mix_list.size(); ++i) {
       input_frames.push_back(rtc::ArrayView<const int16_t>(
           mix_list[i]->data_, samples_per_channel * number_of_channels));
     }
     CombineMultipleFrames(input_frames, audio_frame_for_mixing);
@@ skipping 52 matching lines @@
     // Instead we double the frame (with addition since left-shifting a
     // negative value is undefined).
     AudioFrameOperations::Add(*audio_frame_for_mixing, audio_frame_for_mixing);
   } else {
     std::transform(add_buffer.begin(), add_buffer.begin() + frame_length,
                    audio_frame_for_mixing->data_,
                    [](int32_t a) { return rtc::saturated_cast<int16_t>(a); });
   }
 }
 }  // namespace webrtc