Revert "Address race between device notifications and enumerations in AudioDeviceListenerMac"

This reverts commit 01694e80.

Reason for revert: 
Does not fix the bug it intended to fix.
Reverting will facilitate merging of an alternative patch.


Original change's description:
> Address race between device notifications and enumerations in AudioDeviceListenerMac
> 
> Originally AudioDeviceListenerMac assumed that once CoreAudio reports that a device does not exist,
> it was no longer possible to get notifications related to that device, so it was safe to remove
> the listener for that device.
> However, since notifications can come from multiple threads and the corresponding callbacks make
> a thread jump, we have observed that it is indeed possible to get notifications about removed devices
> which can lead to a crash if the listener for that notification has been removed.
> To address this issue, this CL does not remove listeners when the device is removed, but instead
> marks the listener as deleted and posts a task to remove listeners that have been marked as deleted
> for several seconds, at a time when we can confidently no longer expect notifications from the removed device.
> 
> Bug: 911311
> Change-Id: I07cc9c8e24a0cfdfadcc04d0e8bd33e14ab61422
> Reviewed-on: https://chromium-review.googlesource.com/c/1363187
> Commit-Queue: Guido Urdaneta <guidou@chromium.org>
> Reviewed-by: Oskar Sundbom <ossu@chromium.org>
> Reviewed-by: Olga Sharonova <olka@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#614391}

TBR=guidou@chromium.org,olka@chromium.org,ossu@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 911311
Change-Id: Ic05d999b32ddb308649384ae29c1721d595e6347
Reviewed-on: https://chromium-review.googlesource.com/c/1373840Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615908}

media/audio/mac/audio_device_listener_mac.cc

@@ -12,9 +12,6 @@
 #include "base/mac/mac_logging.h"
 #include "base/optional.h"
 #include "base/single_thread_task_runner.h"
-#include "base/stl_util.h"
-#include "base/threading/thread_task_runner_handle.h"
-#include "base/time/time.h"
 #include "media/audio/audio_manager.h"
 #include "media/audio/mac/core_audio_util_mac.h"
 #include "media/base/bind_to_current_loop.h"
@@ -46,8 +43,6 @@ const AudioObjectPropertyAddress kPropertyInputSourceChanged = {
 
 class AudioDeviceListenerMac::PropertyListener {
  public:
-  static constexpr base::TimeDelta kPruneTime =
-      base::TimeDelta::FromSeconds(15);
   PropertyListener(AudioObjectID monitored_object,
                    const AudioObjectPropertyAddress* property,
                    base::RepeatingClosure callback)
@@ -58,28 +53,13 @@ class AudioDeviceListenerMac::PropertyListener {
   AudioObjectID monitored_object() const { return monitored_object_; }
   const base::RepeatingClosure& callback() const { return callback_; }
   const AudioObjectPropertyAddress* property() const { return address_; }
-  base::TimeTicks deletion_time() const { return deletion_time_; }
-  bool IsActive() const { return deletion_time_.is_null(); }
-  void MarkAsInactive() { deletion_time_ = base::TimeTicks::Now(); }
-  void MarkAsActive() { deletion_time_ = base::TimeTicks(); }
 
  private:
   AudioObjectID monitored_object_;
   const AudioObjectPropertyAddress* address_;
   base::RepeatingClosure callback_;
-  // Stores a deletion time, used for pruning the listener after it is
-  // deregistered from the OS. This helps prevent a race between destroying the
-  // listener after the OS reports the device is removed, and notifications
-  // about the same device that could originate concurrently on another thread.
-  // This can for example, when unplugging a device with input and output
-  // sources, where the noification about source changes might arrive after the
-  // OS reports the device as removed (and therefore marked as deleted). A null
-  // |deletion_time_| means the listener has not been marked as deleted.
-  base::TimeTicks deletion_time_;
 };
 
-constexpr base::TimeDelta AudioDeviceListenerMac::PropertyListener::kPruneTime;
-
 // Callback from the system when an event occurs; this must be called on the
 // MessageLoop that created the AudioManager.
 // static
@@ -188,7 +168,6 @@ void AudioDeviceListenerMac::UpdateSourceListeners() {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
   std::vector<AudioObjectID> device_ids =
       core_audio_mac::GetAllAudioDeviceIDs();
-  bool did_mark_as_deleted = false;
   for (bool is_input : {true, false}) {
     for (auto device_id : device_ids) {
       const AudioObjectPropertyAddress* property_address =
@@ -209,37 +188,15 @@ void AudioDeviceListenerMac::UpdateSourceListeners() {
           } else {
             source_listener.reset();
           }
-        } else {
-          it_key->second->MarkAsActive();
         }
       } else if (is_monitored) {
         // Stop monitoring if the device has no source but is currently being
         // monitored.
         RemovePropertyListener(it_key->second.get());
-        it_key->second->MarkAsInactive();
-        did_mark_as_deleted = true;
+        source_listeners_.erase(it_key);
       }
     }
   }
-  if (did_mark_as_deleted) {
-    base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
-        FROM_HERE,
-        base::BindOnce(&AudioDeviceListenerMac::PruneDeletedListeners,
-                       weak_factory_.GetWeakPtr()),
-        2 * PropertyListener::kPruneTime);
-  }
-}
-
-void AudioDeviceListenerMac::PruneDeletedListeners() {
-  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
-  base::EraseIf(source_listeners_, [](const auto& elem) {
-    if (elem.second->IsActive())
-      return false;
-
-    base::TimeDelta elapsed =
-        base::TimeTicks::Now() - elem.second->deletion_time();
-    return elapsed >= PropertyListener::kPruneTime;
-  });
 }
 
 }  // namespace media

media/audio/mac/audio_device_listener_mac.h

@@ -7,6 +7,7 @@
 
 #include <CoreAudio/AudioHardware.h>
 
+#include <map>
 #include <memory>
 #include <utility>
 
@@ -50,7 +51,6 @@ class MEDIA_EXPORT AudioDeviceListenerMac {
   void RemovePropertyListener(PropertyListener* property_listener);
   void OnDevicesAddedOrRemoved();
   void UpdateSourceListeners();
-  void PruneDeletedListeners();
 
   base::RepeatingClosure listener_cb_;
   std::unique_ptr<PropertyListener> default_output_listener_;