Okay Xcode, whatever you say.
Source list scroll view is layer backed.

This avoids some nasty display glitches during the animation.
Turn on layer backing around the animation.
Force display before the animation.
Bump the xib, apparently.
Don’t embed the scroll view in another view.
Constrain the source list to the desired size.
Don’t embed the source list here either.
Ease in ease out looks better.
Layer back the split view during resize.
Redraw the splitView.
Don’t resize the source list while animating.
Remove the width constraint.
Don’t change translatesAutoresizingMaskIntoConstraints.
Don’t change the autoresizing mask.
Revert "Don’t embed the source list here either."

This reverts commit bd17baf28298202faa23b99cc83a6f30c848d547.
Don’t translate the autoresizing mask.
Do the thing.
Merge pull request #1 from robrix/smooth-animator

Smooth animator