[GStreamer] Fix delayed dispatch of async task post MediaPlayer destruction

https://bugs.webkit.org/show_bug.cgi?id=266715

Reviewed by Xabier Rodriguez-Calvar.

When the media player is destroyed, there can still be async tasks (from AbortableTaskQueue)
ongoing, some of them related to tracks. Those tasks should be aborted, because they depend
on objects that are no longer there.

This patch aborts all pending tasks on AbortableTaskQueue destruction and also unregisters
all pending callbacks from TrackPrivateBaseGStreamer (and asserts that they're no longer
there).

See: #1231

Original author: "Vivek.A" <Vivek_Arumugam@comcast.com>

* Source/WebCore/platform/AbortableTaskQueue.h: Abort tasks on destruction.
* Source/WebCore/platform/graphics/gstreamer/TrackPrivateBaseGStreamer.cpp:
(WebCore::TrackPrivateBaseGStreamer::disconnect): Disconnect handlers and assert.

Canonical link: https://commits.webkit.org/272410@main

Author: varumugam123

Source/WebCore/platform/AbortableTaskQueue.h

@@ -75,6 +75,7 @@ class AbortableTaskQueue final {
         ASSERT(isMainThread());
         ASSERT(!m_lock.isHeld());
         ASSERT(m_channel.isEmpty());
+        startAborting();
     }
 
     // ===========================

Source/WebCore/platform/graphics/gstreamer/TrackPrivateBaseGStreamer.cpp

@@ -142,8 +142,10 @@ TrackPrivateBaseGStreamer::~TrackPrivateBaseGStreamer()
 
 void TrackPrivateBaseGStreamer::disconnect()
 {
-    if (m_stream)
+    if (m_stream) {
         g_signal_handlers_disconnect_matched(m_stream.get(), G_SIGNAL_MATCH_DATA, 0, 0, nullptr, nullptr, this);
+        ASSERT(!g_signal_handler_find(m_stream.get(), G_SIGNAL_MATCH_UNBLOCKED, 0, 0, nullptr, nullptr, nullptr));
+    }
 
     m_tags.clear();
 
@@ -155,8 +157,11 @@ void TrackPrivateBaseGStreamer::disconnect()
         m_bestUpstreamPad.clear();
     }
 
-    if (m_pad)
+    if (m_pad) {
+        g_signal_handlers_disconnect_matched(m_pad.get(), G_SIGNAL_MATCH_DATA, 0, 0, nullptr, nullptr, this);
+        ASSERT(!g_signal_handler_find(m_pad.get(), G_SIGNAL_MATCH_UNBLOCKED, 0, 0, nullptr, nullptr, nullptr));
         m_pad.clear();
+    }
 }
 
 void TrackPrivateBaseGStreamer::tagsChanged()