Ensures that audio tasks cannot run after AudioManager is deleted.

media/audio/alsa/audio_manager_alsa.cc

Index: media/audio/alsa/audio_manager_alsa.cc
diff --git a/media/audio/alsa/audio_manager_alsa.cc b/media/audio/alsa/audio_manager_alsa.cc
index 72c48e3327a88062e87938819bb471d82ff7e6cd..c51d9f04f98b93352c5f73bff7634531fa73dff7 100644
--- a/media/audio/alsa/audio_manager_alsa.cc
+++ b/media/audio/alsa/audio_manager_alsa.cc
@@ -78,15 +78,6 @@ void AudioManagerAlsa::ShowLinuxAudioInputSettings() {
   base::LaunchProcess(command_line, base::LaunchOptions());
 }
 
-// Implementation of AudioManager.
-bool AudioManagerAlsa::HasAudioOutputDevices() {
-  return HasAnyAlsaAudioDevice(kStreamPlayback);
-}
-
-bool AudioManagerAlsa::HasAudioInputDevices() {
-  return HasAnyAlsaAudioDevice(kStreamCapture);
-}
-
 AudioManagerAlsa::AudioManagerAlsa(
     scoped_refptr<base::SingleThreadTaskRunner> task_runner,
     scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner,
@@ -98,8 +89,19 @@ AudioManagerAlsa::AudioManagerAlsa(
   SetMaxOutputStreamsAllowed(kMaxOutputStreams);
 }
 
-AudioManagerAlsa::~AudioManagerAlsa() {
-  Shutdown();
+AudioManagerAlsa::~AudioManagerAlsa() = default;
+
+void AudioManagerAlsa::Shutdown() {
+  AudioManagerBase::Shutdown();
+  wrapper_.reset();
+}
+
+bool AudioManagerAlsa::HasAudioOutputDevices() {
+  return HasAnyAlsaAudioDevice(kStreamPlayback);
+}
+
+bool AudioManagerAlsa::HasAudioInputDevices() {
+  return HasAnyAlsaAudioDevice(kStreamCapture);
 }
 
 void AudioManagerAlsa::ShowAudioInputSettings() {