Google Chrome	69.0.3473.0 (Official Build) dev (64-bit)
Firmware Version Google_Lulu.6301.136.57

Minor issue, might be resolved as by design depending on dev's thoughts. 

Steps to reproduce:
# Enable fullscreen magnifier in settings or via search + ctrl + m
# Use the ctrl + alt + brightness down keys to reduce magnification all the way down
Expected: stops at 2x since that is the minimum magnification in settings 
Actual: goes down to 1x, which in this state, settings reads as "Custom" 

The issue for me is that after this, magnifier remembers the past zoom level making it hard to tell if it is on or off since it's zoomed to 1x. It could leave the user in an ambiguous state.