Ensures that audio tasks cannot run after AudioManager is deleted.

media/audio/audio_system_impl_unittest.cc

Index: media/audio/audio_system_impl_unittest.cc
diff --git a/media/audio/audio_system_impl_unittest.cc b/media/audio/audio_system_impl_unittest.cc
index 26f19873b429029da9ed76986fd47464ee278d3b..a5f147dcb3ac25817d77f2c55195bfc35ead2ab8 100644
--- a/media/audio/audio_system_impl_unittest.cc
+++ b/media/audio/audio_system_impl_unittest.cc
@@ -78,11 +78,12 @@ class AudioSystemImplTest : public testing::TestWithParam<bool> {
   }
 
   ~AudioSystemImplTest() override {
-    // Deleting |audio_manager_| on its thread.
     audio_system_.reset();
     EXPECT_EQ(AudioSystem::Get(), nullptr);
-    audio_manager_.reset();
-    audio_thread_.Stop();
+
+    audio_manager_->GetTaskRunner()->PostTask(
+        FROM_HERE, base::Bind(&media::AudioManager::Shutdown,
+                              base::Unretained(audio_manager_.get())));
   }
 
   void OnAudioParams(const AudioParameters& expected,
@@ -130,9 +131,9 @@ class AudioSystemImplTest : public testing::TestWithParam<bool> {
   base::MessageLoop message_loop_;
   base::ThreadChecker thread_checker_;
   bool use_audio_thread_;
-  base::Thread audio_thread_;
-  MockAudioManager::UniquePtr audio_manager_;
+  std::unique_ptr<media::MockAudioManager> audio_manager_;
   std::unique_ptr<media::AudioSystem> audio_system_;
+  base::Thread audio_thread_;
   AudioParameters input_params_;
   AudioParameters output_params_;
   AudioParameters default_output_params_;