Add support for audio input mute detection on all platforms

media/audio/mac/audio_low_latency_input_mac.cc

Index: media/audio/mac/audio_low_latency_input_mac.cc
diff --git a/media/audio/mac/audio_low_latency_input_mac.cc b/media/audio/mac/audio_low_latency_input_mac.cc
index 1baa09f1fe07f0e2b4d5a89c017eaf53c8a23247..08d40b68f6c5162507d0ee6516f33a54c6d98832 100644
--- a/media/audio/mac/audio_low_latency_input_mac.cc
+++ b/media/audio/mac/audio_low_latency_input_mac.cc
@@ -451,6 +451,34 @@ double AUAudioInputStream::GetVolume() {
   return 0.0;
 }
 
+bool AUAudioInputStream::IsMuted() {
+  // Verify that we have a valid device.
+  if (input_device_id_ == kAudioObjectUnknown) {
+    NOTREACHED() << "Device ID is unknown";

[tommi (sloooow) - chröme, 2014/10/15 17:00:48]

should this be a DCHECK then?

DCHECK_NE(input_device_id_, kAudioObjectUnknown)

+    return false;
+  }
+
+  AudioObjectPropertyAddress property_address = {
+      kAudioDevicePropertyMute,

[tommi (sloooow) - chröme, 2014/10/15 17:00:48]

nit: indent by two spaces and put the closing brace on a line of its own (see
elsewhere in this file)

[henrika (OOO until Aug 14), 2014/10/16 09:58:00]

Done.

+      kAudioDevicePropertyScopeInput,
+      kAudioObjectPropertyElementMaster};
+
+  if (!AudioObjectHasProperty(input_device_id_, &property_address)) {
+    NOTREACHED() << "Device does not support checking master mute state";

[tommi (sloooow) - chröme, 2014/10/15 17:00:48]

since NOTREACHED is essentially the same as DCHECK, I'm wondering if this should
perhaps rather be a DLOG(ERROR)?

[henrika (OOO until Aug 14), 2014/10/16 09:58:00]

Done.

+    return false;
+  }
+
+  UInt32 muted = 0;
+  UInt32 size = sizeof(muted);
+  OSStatus result = AudioObjectGetPropertyData(
+      input_device_id_, &property_address, 0, NULL, &size, &muted);
+  if (result == noErr)
+    return static_cast<bool>(muted);

[tommi (sloooow) - chröme, 2014/10/15 17:00:48]

nit: return muted != 0u;

actually, you could also just do:

DLOG_IF(WARNING, result != noErr) << "Failed to get mute state";
return result == noErr && muted != 0;

[henrika (OOO until Aug 14), 2014/10/16 09:58:00]

Done.

+
+  DLOG(WARNING) << "Failed to get mute state";
+  return false;
+}
+
 // AUHAL AudioDeviceOutput unit callback
 OSStatus AUAudioInputStream::InputProc(void* user_data,
                                        AudioUnitRenderActionFlags* flags,