Add support for audio input mute detection on all platforms

media/audio/cras/cras_input.cc

Index: media/audio/cras/cras_input.cc
diff --git a/media/audio/cras/cras_input.cc b/media/audio/cras/cras_input.cc
index 0b8644603f8996e670b988c282a1b234e4062ee0..3fae8df1e7784dd11462b65c325082080fedabe4 100644
--- a/media/audio/cras/cras_input.cc
+++ b/media/audio/cras/cras_input.cc
@@ -301,6 +301,10 @@ double CrasInputStream::GetVolume() {
   return GetVolumeRatioFromDecibels(dB);
 }
 
+bool CrasInputStream::IsMuted() {
+  return false;
+}
+
 double CrasInputStream::GetVolumeRatioFromDecibels(double dB) const {
   return pow(10, dB / 20.0);
 }