Add a hang monitor for the audio thread.

We've seen a bunch of reports in the field that the audio thread is
getting hung for significant (perhaps indefinite) amounts of time;
to help debug these reports, add a hang monitor which will crash the
browser process and ensure we get a thread dump of what's going on.

The hang timer is set extremely conservatively right now, at 1 minute,
which is insanely long for audio tasks. I'll monitor crash reports and
adjust it as necessary to find culprits.

The hang monitor uses the browser I/O thread for hang checks, which is
similar to what other hung task monitors seem to do. To do this I had
to move AudioManager and MidiManager creation to after the browser
threads have been spun up. Which shouldn't be an issue...

BUG=422522, 469827
TEST=hang time exceeded ==> crash.

Review URL: https://codereview.chromium.org/1036703002

Cr-Commit-Position: refs/heads/master@{#322276}

1 files changed, 7 insertions, 0 deletions

diff --git a/media/audio/audio_manager.h b/media/audio/audio_manager.h
index 7705cdb..5e49b8b 100644
--- a/media/audio/audio_manager.h
+++ b/media/audio/audio_manager.h
@@ -34,6 +34,13 @@ class MEDIA_EXPORT AudioManager {
   // such |audio_log_factory| must outlive the AudioManager.
   static AudioManager* Create(AudioLogFactory* audio_log_factory);
 
+  // Similar to Create() except also schedules a monitor on the given task
+  // runner to ensure the audio thread is not stuck for more than 60 seconds; if
+  // a hang is detected, the process will be crashed.
+  static AudioManager* CreateWithHangTimer(
+      AudioLogFactory* audio_log_factory,
+      const scoped_refptr<base::SingleThreadTaskRunner>& monitor_task_runner);
+
   // Similar to Create() except uses a FakeAudioLogFactory for testing.
   static AudioManager* CreateForTesting();