Restores previously saved focus-related state.
Unpoly automatically restores focus-related state when the user presses the back button.
The viewports for which to restore focus-related state..
Defaults to all viewports within the given layer.
The layer on which to restore focus-related state.
The URL for which to restore focus-related state.
If omitted, the given layer's location is used.
Returns whether focus state could be restored.
