Chrome Version: 65.0.3325.9 (Official Build) dev (64-bit)
OS: ChromeOS

What steps will reproduce the problem?
(1) Configure a keyboard layout that uses AltGraph.
(2) Open https://w3c.github.io/uievents/tools/key-event-viewer.html.
(3) Press the AltGraph key.

What is the expected result?

AltGraph keydown events have only the AltGraph modifier set on them.

What happens instead?

AltGraph keydown events have both Alt and AltGraph modifiers set.
Other AltGraph-shifted events only have AltGraph modifier set.

Not sure precisely when this regressed.