This bothered me as well. It seems like there's no such entry for it in the Chrome Preferences JSON, I assume because it's a macOS-only feature. I've resolved this by creating a Karabiner Elements config which selects the Quit menu item on Command-Q in Chrome. Here's the config in YAML:
- manipulators: - from: key_code: q modifiers: mandatory: - command to: - shell_command: >- osascript -e 'tell application "Google Chrome for Testing" to activate' -e 'tell application "System Events"' -e ' tell process "Google Chrome for Testing"' -e ' click menu item "Quit Chromium" of menu "Google Chrome for Testing" of menu bar 1' -e ' end tell' -e 'end tell' conditions: - type: frontmost_application_if bundle_identifiers: - chrome.for.testing type: basic