Add support for audio input mute detection on all platforms

media/audio/fake_audio_input_stream.cc

Index: media/audio/fake_audio_input_stream.cc
diff --git a/media/audio/fake_audio_input_stream.cc b/media/audio/fake_audio_input_stream.cc
index 74ac579c1a23e1c03bbaa33469a5694c91a18153..157d3978c7613d7f62d39c64e2b8cb656ecd8aa2 100644
--- a/media/audio/fake_audio_input_stream.cc
+++ b/media/audio/fake_audio_input_stream.cc
@@ -203,6 +203,11 @@ double FakeAudioInputStream::GetVolume() {
   return 1.0;
 }
 
+bool FakeAudioInputStream::IsMuted() {
+  DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+  return false;
+}
+
 void FakeAudioInputStream::SetAutomaticGainControl(bool enabled) {}
 
 bool FakeAudioInputStream::GetAutomaticGainControl() {