Are you talking about the black gap underneath the toolbar, like this this screenshot?

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yep. Thanks for the screenshot. I believe (but am not certain) InfoBarBackground::PaintMd is the culprit.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/21e70f121e72154c9891b061e9724ef30e1aecb9

commit 21e70f121e72154c9891b061e9724ef30e1aecb9
Author: estade <estade@chromium.org>
Date: Thu Jul 28 22:25:46 2016

Fix infobar painting issues at fractional scales

This calculates the paths for the infobar background (which paints the arrow) with the scale factor taken into account. It fixes blurriness in the arrow as well as a gap above the infobar (you can see both issues in a screenshot in the linked bug report).

It should have no impact on whole number DSFs (1x, 2x, etc)

BUG= 627601 

Review-Url: https://codereview.chromium.org/2179643002
Cr-Commit-Position: refs/heads/master@{#408498}

[modify] https://crrev.com/21e70f121e72154c9891b061e9724ef30e1aecb9/chrome/browser/ui/views/frame/browser_view_layout.cc
[modify] https://crrev.com/21e70f121e72154c9891b061e9724ef30e1aecb9/chrome/browser/ui/views/infobars/infobar_background.cc

Tested the issue on windows 7 and windows 10(Hi dpi) using chrome version 54.0.2816.0.Still observed gap between toolbar and info bar.Observed the same behaviour with flag --top-chrome-md=material as well.

estade @ Please find the attached screen shot and confirm anything missed here.please provide us any expected screen shot verify from our end.

Thanks,

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That screenshot looks good but it is taken at 1x dsf. You want to test at 1.5x.

Retested the issue at 1.5x using the flag --force-device-scale-factor=1.5 on Win 10 [54.0.2816.0]
Please find the attached screen shots.

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looks right