LibWeb: Move dispatching timeupdate events to a helper for tracking

For some media APIs, we will need to know whether we are currently in an
event handler for the timeupdate event, and the last time we fired the
event.

Userland/Libraries/LibWeb/HTML/HTMLMediaElement.h

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <AK/ByteBuffer.h>
+#include <AK/Time.h>
 #include <AK/Variant.h>
 #include <LibJS/Heap/MarkedVector.h>
 #include <LibJS/SafeFunction.h>
@@ -87,6 +88,8 @@ private:
     void set_paused(bool);
     void set_duration(double);
 
+    WebIDL::ExceptionOr<void> dispatch_time_update_event();
+
     JS::MarkedVector<JS::NonnullGCPtr<WebIDL::Promise>> take_pending_play_promises();
     void resolve_pending_play_promises(ReadonlySpan<JS::NonnullGCPtr<WebIDL::Promise>> promises);
     void reject_pending_play_promises(ReadonlySpan<JS::NonnullGCPtr<WebIDL::Promise>> promises, JS::NonnullGCPtr<WebIDL::DOMException> error);
@@ -126,6 +129,9 @@ private:
     // https://html.spec.whatwg.org/multipage/media.html#media-data
     ByteBuffer m_media_data;
 
+    bool m_running_time_update_event_handler { false };
+    Optional<Time> m_last_time_update_event_time;
+
     JS::GCPtr<Fetch::Infrastructure::FetchController> m_fetch_controller;
 };