These errors are spit out:

[7403:775:1213/115335.218643:ERROR:scoped_audio_unit.cc(43)] Failed to set current device for audio unit.: Error Domain=NSOSStatusErrorDomain Code=-10851 "(null)" (-10851)
[7403:775:1213/115335.218739:ERROR:audio_manager_mac.cc(634)] Failed to get the device channels, use stereo as default for device default
[7403:775:1213/115335.220171:ERROR:scoped_audio_unit.cc(43)] Failed to set current device for audio unit.: Error Domain=NSOSStatusErrorDomain Code=-10851 "(null)" (-10851)
[7403:775:1213/115335.220204:ERROR:audio_manager_mac.cc(634)] Failed to get the device channels, use stereo as default for device AppleHDAEngineInput:1F,3,0,1,0:1
[7403:775:1213/115335.221032:ERROR:scoped_audio_unit.cc(43)] Failed to set current device for audio unit.: Error Domain=NSOSStatusErrorDomain Code=-10851 "(null)" (-10851)
[7403:775:1213/115335.221069:ERROR:audio_manager_mac.cc(634)] Failed to get the device channels, use stereo as default for device AppleUSBAudioEngine:Unknown Manufacturer:Jabra SPEAK 410 USB:1C48F959BFE4x010900:2
[7403:775:1213/115335.224960:ERROR:scoped_audio_unit.cc(43)] Failed to set current device for audio unit.: Error Domain=NSOSStatusErrorDomain Code=-10851 "(null)" (-10851)
[7403:775:1213/115335.225004:ERROR:audio_manager_mac.cc(634)] Failed to get the device channels, use stereo as default for device default

I saw that IO is not enabled on input, which is required before setting the current device. I fixed that and instead the failures:

[10525:775:1213/132413.043872:ERROR:audio_manager_mac.cc(379)] Failed to get property info for AudioUnit channel layout.: Error Domain=NSOSStatusErrorDomain Code=-10879 "(null)" (-10879)
[10525:775:1213/132413.044172:ERROR:audio_manager_mac.cc(634)] Failed to get the device channels, use stereo as default for device default
[10525:775:1213/132413.045529:ERROR:audio_manager_mac.cc(379)] Failed to get property info for AudioUnit channel layout.: Error Domain=NSOSStatusErrorDomain Code=-10879 "(null)" (-10879)
[10525:775:1213/132413.045781:ERROR:audio_manager_mac.cc(634)] Failed to get the device channels, use stereo as default for device AppleHDAEngineInput:1F,3,0,1,0:1
[10525:775:1213/132413.047281:ERROR:audio_manager_mac.cc(379)] Failed to get property info for AudioUnit channel layout.: Error Domain=NSOSStatusErrorDomain Code=-10879 "(null)" (-10879)
[10525:775:1213/132413.047534:ERROR:audio_manager_mac.cc(634)] Failed to get the device channels, use stereo as default for device AppleUSBAudioEngine:Unknown Manufacturer:Jabra SPEAK 410 USB:1C48F959BFE4x010900:2
[10525:775:1213/132413.059119:ERROR:audio_manager_mac.cc(379)] Failed to get property info for AudioUnit channel layout.: Error Domain=NSOSStatusErrorDomain Code=-10879 "(null)" (-10879)
[10525:775:1213/132413.059387:ERROR:audio_manager_mac.cc(634)] Failed to get the device channels, use stereo as default for device default

The failure is kAudioUnitErr_InvalidProperty, which to the best of my knowledge means that the property isn't relevant for that element & scope on that AudioUnit. (Input element, output scope in this case.) As a verification, changing scope gives kAudioUnitErr_InvalidElement. It would make sense that channel layout isn't relevant for the input element.

Using GetDeviceTotalChannelCount() in AudioManagerMac, which we already call before getting the layout, for number of input channels should fix this. I wrote a CL for that: https://chromium-review.googlesource.com/c/chromium/src/+/823972

Dale: can you have a look since you wrote the change in how we get the number of channels? Would you say my conclusion in #1 is correct?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3ccfcbbac6f7055e92d9da39be10c656617468fb

commit 3ccfcbbac6f7055e92d9da39be10c656617468fb
Author: Henrik Grunell <grunell@chromium.org>
Date: Wed Dec 20 12:52:13 2017

Fix for getting number of audio input channels on Mac.

Don't get channel layout for input element since that's not supported on AUHAL[1], instead get the channel count from the stream layout.

Plus fixes in ScopedAudioUnit:
* Enable IO before setting current device which is a requirement.
* Use element 0 with global scope, which is the element to use with that scope. (This didn't cause a failure.)

[1] Follow-up on this to confirm: https://crbug.com/796163

Bug:  794501 
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I3879989e30449000dc9d75f756c69738ac54615a
Reviewed-on: https://chromium-review.googlesource.com/823972
Commit-Queue: Henrik Grunell <grunell@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525314}
[modify] https://crrev.com/3ccfcbbac6f7055e92d9da39be10c656617468fb/media/audio/mac/audio_auhal_mac.cc
[modify] https://crrev.com/3ccfcbbac6f7055e92d9da39be10c656617468fb/media/audio/mac/audio_manager_mac.cc
[modify] https://crrev.com/3ccfcbbac6f7055e92d9da39be10c656617468fb/media/audio/mac/scoped_audio_unit.cc