How can I view the original (or "master") version of a photo in Photos without reverting all edits? Most photo applications provides some way to toggle between the original (unedited) version of a photo and the current (edited) one.  

In Aperture, "M" toggles between the two, many iOS photo apps let you touch the screen to compare the edited or filtered version to the original, etc.

I can't find any way to show the original in the new Photos app other than "reverting," which removes all the edits.

I don't want to remove them, I just want to compare the two.  

I realize that I can "revert" then undo, but it's hacky, slow, and worse, dangerous - counting on undo to preserve work in any app is iffy, at best.

Note: The fact that Aperture edits are saved "less destructively" than Photos shouldn't be relevant here.  Both applications DO retain the original, in edition to the edited version.
While in Edit mode, hold down the Control and M keys.

This will show you the original version of your photo, with no edits applied. If you want to temporarily undo the effect of the color adjustments but keep the cropping and rotation the same, hold down M by itself.

Unlike Aperture:


It doesn’t work in “view mode”; you have to be in edit mode. (To get into edit mode via the keyboard, press Return.)
It’s a hold, not a toggle, so you only see the original photo for as long as you have the keys held down.