The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/adhd/+/b9bf4e351d33213f6bd9896b53bb1ff7fde509c0

commit b9bf4e351d33213f6bd9896b53bb1ff7fde509c0
Author: Hsin-Yu Chao <hychao@chromium.org>
Date: Thu May 05 09:16:57 2016

CRAS: iodev - Avoid set volume loop by Chrome UI

When a node's volume is changed by a component different than
Chrome, dbus signal 'OutputNodeVolumeChanged' will be fired.
If Chrome wasn't synced about the new volume, it could try to
tell CRAS to update volume again.  Avoid this set volume loop
by adding a check to node's volume attribute.

BUG= chromium:609458 
TEST=Use cras_test_client to set the same node volume multiple
times, verify there is only one dbus signal fired.

Change-Id: Iac57b510fa2fb350462325fc9b69fcc6c0044077
Reviewed-on: https://chromium-review.googlesource.com/342766
Commit-Ready: Hsinyu Chao <hychao@chromium.org>
Tested-by: Hsinyu Chao <hychao@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>

[modify] https://crrev.com/b9bf4e351d33213f6bd9896b53bb1ff7fde509c0/cras/src/server/cras_iodev.c

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/system_api/+/ce15e6137e183e93557ff34cac95fb5b67355a81

commit ce15e6137e183e93557ff34cac95fb5b67355a81
Author: Hsin-Yu Chao <hychao@chromium.org>
Date: Mon May 09 03:50:08 2016

service_constants: Add kOutputNodeVolumeChanged signal

This signal will be monitored by Chrome UI to synchronize
volume when the hardware changes its volume.

BUG= chromium:609458 
TEST=None

Change-Id: I9762b60b10eb96e2e4ac7731504a6ce33d604987
Reviewed-on: https://chromium-review.googlesource.com/343326
Commit-Ready: Hsinyu Chao <hychao@chromium.org>
Tested-by: Hsinyu Chao <hychao@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>

[modify] https://crrev.com/ce15e6137e183e93557ff34cac95fb5b67355a81/dbus/service_constants.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/232822b744f33bce79ae0fbfa2a2bf9d21a91bec

commit 232822b744f33bce79ae0fbfa2a2bf9d21a91bec
Author: hychao <hychao@chromium.org>
Date: Wed May 18 18:44:50 2016

Roll cros_syste_api DEPS.

Roll cros_system_api to 534baa06 to get new CRAS signal name.

BUG= 609458 
R=derat@chromium.org

Review-Url: https://codereview.chromium.org/1971073002
Cr-Commit-Position: refs/heads/master@{#394481}

[modify] https://crrev.com/232822b744f33bce79ae0fbfa2a2bf9d21a91bec/DEPS

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7a0ee45432bf8e1c284216525de2d49421cc3e78

commit 7a0ee45432bf8e1c284216525de2d49421cc3e78
Author: hychao <hychao@chromium.org>
Date: Thu May 19 11:29:10 2016

When a headset or other application changes the active node's
volume on system, Chrome UI should know that and updates the
stored volume accordingly.

BUG= 609458 
TEST=Run cras_test_client --set_node_volume on the active node
to verify Chrome UI shows volume bar to reflect the change.

Review-Url: https://codereview.chromium.org/1952983002
Cr-Commit-Position: refs/heads/master@{#394738}

[modify] https://crrev.com/7a0ee45432bf8e1c284216525de2d49421cc3e78/chromeos/audio/cras_audio_handler.cc
[modify] https://crrev.com/7a0ee45432bf8e1c284216525de2d49421cc3e78/chromeos/audio/cras_audio_handler.h
[modify] https://crrev.com/7a0ee45432bf8e1c284216525de2d49421cc3e78/chromeos/dbus/cras_audio_client.cc
[modify] https://crrev.com/7a0ee45432bf8e1c284216525de2d49421cc3e78/chromeos/dbus/cras_audio_client.h
[modify] https://crrev.com/7a0ee45432bf8e1c284216525de2d49421cc3e78/chromeos/dbus/cras_audio_client_unittest.cc

This might have caused this issue https://bugs.chromium.org/p/chromium/issues/detail?id=614885

Verified on build 8844.0.0