Add support for audio input mute detection on all platforms

media/audio/mac/audio_input_mac.cc

Index: media/audio/mac/audio_input_mac.cc
diff --git a/media/audio/mac/audio_input_mac.cc b/media/audio/mac/audio_input_mac.cc
index b7f6e17310954e5ef3aa04dce96c76831640f2bf..af5d9bc16e591d51875fcb516d1bdec8bece656e 100644
--- a/media/audio/mac/audio_input_mac.cc
+++ b/media/audio/mac/audio_input_mac.cc
@@ -136,6 +136,11 @@ double PCMQueueInAudioInputStream::GetVolume() {
   return 0.0;
 }
 
+bool PCMQueueInAudioInputStream::IsMuted() {
+  NOTREACHED() << "Only supported for low-latency mode.";
+  return false;
+}
+
 void PCMQueueInAudioInputStream::SetAutomaticGainControl(bool enabled) {
   NOTREACHED() << "Only supported for low-latency mode.";
 }