LibWeb: Report HTMLMediaElement duration with sub-second accuracy

We currently use Time::to_seconds() to report a video's duration. The
video, however, may have a sub-second duration. For example, the video
used by the video test page is 12.05 seconds long.

Userland/Libraries/LibWeb/HTML/HTMLMediaElement.cpp

@@ -676,7 +676,8 @@ WebIDL::ExceptionOr<void> HTMLMediaElement::process_media_data(Function<void()>
         // 4. Update the duration attribute with the time of the last frame of the resource, if known, on the media timeline established above. If it is
         //    not known (e.g. a stream that is in principle infinite), update the duration attribute to the value positive Infinity.
         // FIXME: Handle unbounded media resources.
-        set_duration(static_cast<double>(video_track->duration().to_seconds()));
+        auto duration = static_cast<double>(video_track->duration().to_milliseconds());
+        set_duration(duration / 1000.0);
 
         // 5. For video elements, set the videoWidth and videoHeight attributes, and queue a media element task given the media element to fire an event
         //    named resize at the media element.