Ensures that audio tasks cannot run after AudioManager is deleted.

content/browser/renderer_host/media/audio_renderer_host_unittest.cc

Index: content/browser/renderer_host/media/audio_renderer_host_unittest.cc
diff --git a/content/browser/renderer_host/media/audio_renderer_host_unittest.cc b/content/browser/renderer_host/media/audio_renderer_host_unittest.cc
index 20ea45557eb243a36ef6ec40955a899fecfa02bd..5b2e73780368550dcfb4cf5661c25a1c4f638574 100644
--- a/content/browser/renderer_host/media/audio_renderer_host_unittest.cc
+++ b/content/browser/renderer_host/media/audio_renderer_host_unittest.cc
@@ -257,11 +257,10 @@ class AudioRendererHostTest : public testing::Test {
     // Simulate closing the IPC channel and give the audio thread time to close
     // the underlying streams.
     host_->OnChannelClosing();
+    audio_manager_->GetTaskRunner()->PostTask(
+        FROM_HERE, base::Bind(&media::AudioManager::Shutdown,
+                              base::Unretained(audio_manager_.get())));
     SyncWithAudioThread();
-    // To correctly clean up the audio manager, we first put it in a
-    // ScopedAudioManagerPtr. It will immediately destruct, cleaning up the
-    // audio manager correctly.
-    media::ScopedAudioManagerPtr(audio_manager_.release());
 
     // Release the reference to the mock object.  The object will be destructed
     // on message_loop_.