Support animations where we want to animate a snapshot of the content of a ServerWindow such that changes to the ServerWindow itself (including the window destruction) do not interfere with the animation. E.g.:
 - Close animation: Transform + opacity animation of the window content, while the window itself is getting destroyed.
 - Resize animation: Capture the window content, layout the window using the new bounds, perform a cross-fade animation of the old window content and the new window content.

Rough design doc: https://docs.google.com/document/d/1sf2UW4SXMwW1Skicus4_6A3hyQyxZMG19XZlLbzG74U/edit