LibWeb: Abort media element resource selection upon loading a source

This fixes a crash when playing video on The Cutting Room Floor.

Without aborting the resource selection algorithm, two resource
selection algorithms could be running at once, resulting in the
element requesting removal of a track from the PlaybackManager
immediately after it had been replaced with a different instance.
PlaybackManager asserts that removal of a track is valid, so this was
causing a WebContent crash.

Author: Zaggy1024

Libraries/LibWeb/HTML/HTMLMediaElement.cpp

@@ -531,7 +531,11 @@ WebIDL::ExceptionOr<void> HTMLMediaElement::load_element()
 {
     m_first_data_load_event_since_load_start = true;
 
-    // FIXME: 1. Abort any already-running instance of the resource selection algorithm for this element.
+    // 1. Abort any already-running instance of the resource selection algorithm for this element.
+    //    NOTE: All deferred subroutines of the resource selection algorithm will be queued under the media element task
+    //          source, or run as part of the fetch. Step 2 will remove any subroutine from the queue. Step 6.2 will stop
+    //          any ongoing fetch operation. Therefore, all resource selection algorithms will be cancelled before a new
+    //          one begins.
 
     // 2. Let pending tasks be a list of all tasks from the media element's media element event task source in one of the task queues.
     [[maybe_unused]] auto pending_tasks = HTML::main_thread_event_loop().task_queue().take_tasks_matching([&](auto& task) {
@@ -827,7 +831,7 @@ WebIDL::ExceptionOr<void> HTMLMediaElement::select_resource()
     // 4. Await a stable state, allowing the task that invoked this algorithm to continue. The synchronous section consists of all the remaining
     // steps of this algorithm until the algorithm says the synchronous section has ended. (Steps in synchronous sections are marked with ⌛.)
 
-    queue_a_microtask(&document(), GC::create_function(realm.heap(), [this, &realm]() {
+    queue_a_media_element_task([this, &realm]() {
         // FIXME: 5. ⌛ If the media element's blocked-on-parser flag is false, then populate the list of pending text tracks.
 
         Optional<SelectMode> mode;
@@ -917,12 +921,12 @@ WebIDL::ExceptionOr<void> HTMLMediaElement::select_resource()
 
             // 5. If urlRecord was obtained successfully, run the resource fetch algorithm with urlRecord. If that algorithm returns without aborting this one,
             //    then the load failed.
-            Platform::EventLoopPlugin::the().deferred_invoke(GC::create_function(realm.heap(), [this, url_record = move(url_record), failed_with_attribute = move(failed_with_attribute)]() mutable {
+            queue_a_media_element_task([this, url_record = move(url_record), failed_with_attribute = move(failed_with_attribute)]() mutable {
                 if (url_record.has_value()) {
                     fetch_resource(*url_record, move(failed_with_attribute)).release_value_but_fixme_should_propagate_errors();
                     return;
                 }
-            }));
+            });
 
             // 8. Return. The element won't attempt to load another resource until this algorithm is triggered again.
             return;
@@ -957,7 +961,7 @@ WebIDL::ExceptionOr<void> HTMLMediaElement::select_resource()
 
             break;
         }
-    }));
+    });
 
     return {};
 }