Fix zero channel count being returned for unknown macOS layouts.

media/audio/mac/audio_manager_mac.cc

Index: media/audio/mac/audio_manager_mac.cc
diff --git a/media/audio/mac/audio_manager_mac.cc b/media/audio/mac/audio_manager_mac.cc
index 436d4ee77bcb3e6fb2413de73e3b68b053a5357f..cb2ac1f1f2f7b8fce551096508bcafee56560f7c 100644
--- a/media/audio/mac/audio_manager_mac.cc
+++ b/media/audio/mac/audio_manager_mac.cc
@@ -447,8 +447,10 @@ bool AudioManagerMac::GetDeviceChannels(AudioDeviceID device,
   // only return up to 8 channels in any layout. To allow WebAudio to work with
   // > 8 channel devices, we must use the total channel count instead of the
   // channel count of the preferred layout.
-  if (GetDeviceTotalChannelCount(device, scope, channels) &&
-      *channels > kMaxConcurrentChannels) {
+  int total_channel_count = 0;
+  if (GetDeviceTotalChannelCount(device, scope, &total_channel_count) &&
+      total_channel_count > kMaxConcurrentChannels) {
+    *channels = total_channel_count;
     return true;
   }
 
@@ -510,6 +512,12 @@ bool AudioManagerMac::GetDeviceChannels(AudioDeviceID device,
     }
   }
 
+  // If we still don't have a channel count, fall back to total channel count.
+  if (*channels == 0) {
+    DLOG(WARNING) << "Unable to use channel layout for channel count.";
+    *channels = total_channel_count;
+  }
+
   DVLOG(1) << (scope == kAudioDevicePropertyScopeInput ? "Input" : "Output")
            << " channels: " << *channels;
   return true;