bug#51883: 29.0.50; Command to get accidentally deleted frames back

[Gregory Heytings]

> The command sounds useful, but I worry about one possible problem: how 
> much garbage will the to-be-restored frame hold onto? Please investigate 
> this and see whether it is a significant issue or not.

It's not significant.  The frames are not kept in memory for later 
possible reuse, only a description of their state (size, windows, which 
buffer is displayed in which window) is kept in memory, which occupies a 
few kilobytes for each deleted frame.  That's much less than the memory 
used by undo, for example.  Moreover that state would not be kept for all 
deleted frames, but only for a the most recently deleted ones.