Fixed in https://chromium-review.googlesource.com/c/chromium/src/+/1205671

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7790d54ffed5d70ef5655d018bd4fb7786207842

commit 7790d54ffed5d70ef5655d018bd4fb7786207842
Author: kristipark <kristipark@chromium.org>
Date: Wed Sep 05 13:55:39 2018

[NTP] Center edit custom link dialog in the viewport

Centers the dialog in the viewport rather than the ntp-contents div.

Before: https://screenshot.googleplex.com/kk5zQAxuCTr.png
After: https://screenshot.googleplex.com/NE4asURv2Dp.png

Bug:  880582 
Change-Id: If5eac9aaf3bfd1d8e778aa684d6acffd874bab6d
Reviewed-on: https://chromium-review.googlesource.com/1205671
Commit-Queue: Mathieu Perreault <mathp@chromium.org>
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588851}
[modify] https://crrev.com/7790d54ffed5d70ef5655d018bd4fb7786207842/chrome/browser/resources/local_ntp/local_ntp.css

Able to reproduce this issue on build without fix hence verifying the fix on latest canary 71.0.3544.0 using Mac 10.13.6, Windows 10 and Debian.

Now Edit custom link is seen centered in the viewport . Attaching screenshots for reference.

As fix is working as expected adding Verified labels.

Thanks!

Deleted: Center aligned_withfix.png 284 KB

	Center aligned_withfix.png 284 KB View Download