crash-reporter: Add a missing Chrome thread to ignore

I somehow missed "AudioOutputDevice" as the name of a Chrome thread.  It
showed up in crash reports.

BUG=chrome-os-partner:12045
TEST=Ran unittests

Change-Id: Ia29404aebfe806a81fceb6b45145434af6749822
Reviewed-on: https://gerrit.chromium.org/gerrit/33224
Commit-Ready: Michael Krebs <mkrebs@chromium.org>
Tested-by: Michael Krebs <mkrebs@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
diff --git a/crash_reporter/user_collector.cc b/crash_reporter/user_collector.cc
index c96d272..d3ee66d 100644
--- a/crash_reporter/user_collector.cc
+++ b/crash_reporter/user_collector.cc
@@ -572,7 +572,7 @@
     /* These come from the use of base::Watchdog */
     "Startup watchdog thread Watchdog", "Shutdown watchdog thread Watchdog",
     /* These come from the use of AudioDeviceThread::Start */
-    "AudioDevice", "AudioInputDevice",
+    "AudioDevice", "AudioInputDevice", "AudioOutputDevice",
     /* These come from the use of MessageLoopFactory::GetMessageLoop */
     "GpuVideoDecoder", "RtcVideoDecoderThread", "PipelineThread",
     "AudioDecoderThread", "VideoDecoderThread",