Switch audio hang monitor to default-off. Enable for non-beta,stable.

Too many crashes and out of ideas for how to resolve this for right
now; this at least provides the chance that these users might unhang
themselves some time after the 2 minute hang timer.

BUG=422522, 468074, 478932
TEST=start w/ and w/o hang monitor according to channel, flags.

Review URL: https://codereview.chromium.org/1105083004

Cr-Commit-Position: refs/heads/master@{#327356}

chrome/browser/DEPS

@@ -116,6 +116,7 @@ include_rules = [
   "+grit",  # TODO(thestig) Remove. For generated headers
   "+installer_util_strings",  # For generated headers
   "+jni",
+  "+media/audio", # For media audio hang monitor.
   "+media/base",  # For media switches
   "+policy",  # For generated headers and source
   "+ppapi/c",  # For various types.

chrome/browser/chrome_browser_main.cc

@@ -134,6 +134,7 @@
 #include "content/public/common/content_switches.h"
 #include "content/public/common/main_function_params.h"
 #include "grit/platform_locale_settings.h"
+#include "media/audio/audio_manager.h"
 #include "net/base/net_module.h"
 #include "net/cookies/cookie_monster.h"
 #include "net/http/http_network_layer.h"
@@ -673,8 +674,18 @@ void ChromeBrowserMainParts::SetupMetricsAndFieldTrials() {
   // Now that field trials have been created, initializes metrics recording.
   metrics->InitializeMetricsRecordingState();
 
+  const chrome::VersionInfo::Channel channel =
+      chrome::VersionInfo::GetChannel();
+
+  // TODO(dalecurtis): Remove these checks and enable for all channels once we
+  // track down the root causes of crbug.com/422522 and crbug.com/478932.
+  if (channel == chrome::VersionInfo::CHANNEL_UNKNOWN ||
+      chrome::VersionInfo::CHANNEL_CANARY || chrome::VersionInfo::CHANNEL_DEV) {
+    media::AudioManager::EnableHangMonitor();
+  }
+
   // Enable profiler instrumentation depending on the channel.
-  switch (chrome::VersionInfo::GetChannel()) {
+  switch (channel) {
     case chrome::VersionInfo::CHANNEL_UNKNOWN:
     case chrome::VersionInfo::CHANNEL_CANARY:
       tracked_objects::ScopedTracker::Enable();

media/audio/audio_manager.cc

@@ -6,6 +6,7 @@
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
+#include "base/command_line.h"
 #include "base/debug/alias.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
@@ -14,6 +15,7 @@
 #include "build/build_config.h"
 #include "media/audio/audio_manager_factory.h"
 #include "media/audio/fake_audio_log_factory.h"
+#include "media/base/media_switches.h"
 
 namespace media {
 namespace {
@@ -131,6 +133,8 @@ class AudioManagerHelper : public base::PowerObserver {
   DISALLOW_COPY_AND_ASSIGN(AudioManagerHelper);
 };
 
+static bool g_hang_monitor_enabled = false;
+
 static base::LazyInstance<AudioManagerHelper>::Leaky g_helper =
     LAZY_INSTANCE_INITIALIZER;
 }  // namespace
@@ -177,11 +181,11 @@ AudioManager* AudioManager::CreateWithHangTimer(
     AudioLogFactory* audio_log_factory,
     const scoped_refptr<base::SingleThreadTaskRunner>& monitor_task_runner) {
   AudioManager* manager = Create(audio_log_factory);
-  // On OSX the audio thread is the UI thread, for which a hang monitor is not
-  // necessary.
-#if !defined(OS_MACOSX)
+  if (g_hang_monitor_enabled ||
+      base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableAudioHangMonitor)) {
     g_helper.Pointer()->StartHangTimer(monitor_task_runner);
-#endif
+  }
   return manager;
 }
 
@@ -190,6 +194,17 @@ AudioManager* AudioManager::CreateForTesting() {
   return Create(g_helper.Pointer()->fake_log_factory());
 }
 
+// static
+void AudioManager::EnableHangMonitor() {
+  CHECK(!g_last_created);
+// On OSX the audio thread is the UI thread, for which a hang monitor is not
+// necessary or recommended.  If it's manually requested, we should allow it
+// to start though.
+#if !defined(OS_MACOSX)
+  g_hang_monitor_enabled = true;
+#endif
+}
+
 // static
 AudioManager* AudioManager::Get() {
   return g_last_created;

media/audio/audio_manager.h

@@ -47,7 +47,7 @@ class MEDIA_EXPORT AudioManager {
 
   // 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.
+  // a hang is detected, the process will be crashed.  See EnableHangMonitor().
   static AudioManager* CreateWithHangTimer(
       AudioLogFactory* audio_log_factory,
       const scoped_refptr<base::SingleThreadTaskRunner>& monitor_task_runner);
@@ -55,6 +55,12 @@ class MEDIA_EXPORT AudioManager {
   // Similar to Create() except uses a FakeAudioLogFactory for testing.
   static AudioManager* CreateForTesting();
 
+  // Enables the hang monitor for the AudioManager once it's created.  Must be
+  // called before the AudioManager is created.  CreateWithHangTimer() requires
+  // either switches::kEnableAudioHangMonitor to be present or this to have been
+  // called previously to start the hang monitor.  Does nothing on OSX.
+  static void EnableHangMonitor();
+
   // Should only be used for testing. Resets a previously-set
   // AudioManagerFactory. The instance of AudioManager is not affected.
   static void ResetFactoryForTesting();

media/base/media_switches.cc

@@ -84,6 +84,11 @@ const char kWaveOutBuffers[] = "waveout-buffers";
 const char kUseCras[] = "use-cras";
 #endif
 
+// Enables the audio thread hang monitor.  Allows us to find users in the field
+// who have stuck audio threads.  See crbug.com/422522 and crbug.com/478932.
+// TODO(dalecurtis): This should be removed once those issues are resolved.
+const char kEnableAudioHangMonitor[] = "enable-audio-hang-monitor";
+
 // Use fake device for Media Stream to replace actual camera and microphone.
 const char kUseFakeDeviceForMediaStream[] = "use-fake-device-for-media-stream";
 

media/base/media_switches.h

@@ -46,6 +46,8 @@ MEDIA_EXPORT extern const char kWaveOutBuffers[];
 MEDIA_EXPORT extern const char kUseCras[];
 #endif
 
+MEDIA_EXPORT extern const char kEnableAudioHangMonitor[];
+
 MEDIA_EXPORT extern const char kUseFakeDeviceForMediaStream[];
 MEDIA_EXPORT extern const char kUseFileForFakeVideoCapture[];
 MEDIA_EXPORT extern const char kUseFileForFakeAudioCapture[];