Add mute state field to AudioFrame.

webrtc/modules/audio_mixer/sine_wave_generator.cc

Index: webrtc/modules/audio_mixer/sine_wave_generator.cc
diff --git a/webrtc/modules/audio_mixer/sine_wave_generator.cc b/webrtc/modules/audio_mixer/sine_wave_generator.cc
index f16312f1db8fc4a9e6cf220bb3d13e25a7ef3517..f295045de0ab152b04f74ed32d8670de20597215 100644
--- a/webrtc/modules/audio_mixer/sine_wave_generator.cc
+++ b/webrtc/modules/audio_mixer/sine_wave_generator.cc
@@ -22,9 +22,10 @@ constexpr float kPi = 3.14159265f;
 
 void SineWaveGenerator::GenerateNextFrame(AudioFrame* frame) {
   RTC_DCHECK(frame);
+  int16_t* frame_data = frame->mutable_data();
   for (size_t i = 0; i < frame->samples_per_channel_; ++i) {
     for (size_t ch = 0; ch < frame->num_channels_; ++ch) {
-      frame->data_[frame->num_channels_ * i + ch] =
+      frame_data[frame->num_channels_ * i + ch] =
           rtc::saturated_cast<int16_t>(amplitude_ * sinf(phase_));
     }
     phase_ += wave_frequency_hz_ * 2 * kPi / frame->sample_rate_hz_;