Fix messages window scroll jumping up when hovering the dragbar

[nevkontakte]

[flackr]

Can we fix this instead by making .dragbar transform: scale(6, 1) (or something like that) instead of animating width and margin-right? Even though what you've done effectively makes it not relayout the chat area (because dragbar still consumes the same total width) it still does require a layout pass and doing the animation on the main thread where the transform animation can be done on the compositor.