Bisected to fab6a4eec6cb6b40e9931465bbc90d545a6d40ed = https://crrev.com/1859283003 by jbauman@chromium.org
"Avoid restoring maximized window down when going fullscreen."
Landed in 52.0.2707.0

Repro: use the attached test.html and run chrome test.html --start-maximized --start-fullscreen
Expected: numbers are equal
Observed: numbers are different

Deleted: test.html 563 bytes

test.html 563 bytes View Download

Able to reproduce the issue on Win-10 using chrome reported version #66.0.3359.139 and latest canary #68.0.3431.0.
This is a non-regression issue as it is observed from M60 old builds. Issue is not reproducible in OS-mac and OS-linux i.e window.outerWidth/Height is more than 16px than should be when in fullscreen mode (using F11-key).

Hence, marking it as untriaged to get more inputs from dev team.

Thanks...!!

Confirmed, seems limited to windows. I'm guessing we incorrectly subtract the scrollbar width in fullscreen (but not in regular mode).
This is quite odd.

szager, any idea why this might be?

If it was 15px, I would guess scrollbar; but because it's 16px, I wonder if it has something to do with body padding?

It's happens with the height as well (same 16px).

The observed 16px difference is produced by the default 8px border of the window.
My desktop theme has a smaller 4px border, which explains why I see 8px difference.

In my situation (Win10) I have:
- no borders (only tabs and address bar at the top in maximized mode and nothing in fullscreen mode of course)
- no scrollbars visible (empty page with CSS: *{margin:0;padding:0;} )
- screen resolution = 1920x1080 (standard laptop screen)
- screen.width & .height are 1920 and 1080

Normal mode with maximized window:
- window.outerWidth == 1920
- window.outerHeight == 1040

After entering fullscreen mode with [F11]:
- window.outerWidth == 1904
- window.outerHeight == 1064

The bug doesn't need the window borders to be actually visible.
Chrome (or OS) just blindly subtracts their width which is 2*GetSystemMetrics(SM_CXPADDEDBORDER)

In Windows 10 it can be changed via PaddedBorderWidth in the registry AFAIK.
In Windows 7 it's relatively easy to change as "Active window border" in the legacy desktop control panel.
When I change it, the outerWidth gap changes accordingly and matches the above formula.