How to reproduce

• Leaflet version I'm using: 1.2.0
• Browser (with version) I'm using: Chrome 60
• OS/Platform (with version) I'm using: Linux
• Open VideoOverlay example
• Zoom map with video overlay

What behaviour I'm expecting and which behaviour I'm seeing

Expecting VideoOverlay to animate as smooth as map tiles.
Instead, VideoOverlay jumps without animation.

It was broken in #5731 (first parameter in DomUtil.addClass function is missing).