Able reproduce this on the latest canary(54.0.2799.0) on Windows-7 and Mac OS 10.11.5 as well.

CHANGELOG URL:
  https://chromium.googlesource.com/chromium/src/+log/8c8fcf75d3d52895282a8a8f1ed17491fd66ea82..52116563313f1ebe1e2b966b429d217442e3362b


Suspecting https://codereview.chromium.org/2062353002 from changelog.

@j.isorce: Please help in re-assigning if it is not related to your change.

Good Build: 54.0.2797.0 dev
Bad Build: 54.0.2798.0 dev

Issue is also seen using some other steps.

1.Classic theme >> Open Incognito window >> Observe bookmark bar when it is detached

2. Issue is also seen on adding https://chrome.google.com/webstore/detail/city-and-bridge-in-the-fo/kdegpmcndhhenlehkilbepaihkaefkom?utm_source=chrome-ntp-icon

Deleted: CLassic theme.png 100 KB

	CLassic theme.png 100 KB View Download

Deleted: bookmarkbar1.png 1.1 MB

	bookmarkbar1.png 1.1 MB View Download

Hi, yes this related to my change https://codereview.chromium.org/2062353002/ 

Thx for the theme link to reproduce the pb in normal browsing. The steps with incognito mode have been already reported here https://bugs.chromium.org/p/chromium/issues/detail?id=618335

I can reproduce both on Linux. I will have a look but I need to speak with Peter too. Worst case I will revert it.

In the mean time one is welcome to help making a unit test for it. Thx.

To help debugging the following change put back old behavior for both cases mentioned previously (theme and incognito):

--- a/chrome/browser/ui/views/frame/browser_view.cc
+++ b/chrome/browser/ui/views/frame/browser_view.cc
@@ -223,7 +223,7 @@ void PaintDetachedBookmarkBar(gfx::Canvas* canvas,
   // The detached bar overlaps the |contents_container_| and so uses the same
   // background color (the NTP background color).
   canvas->FillRect(fill_rect,
-                   tp->GetColor(ThemeProperties::COLOR_NTP_BACKGROUND));
+                   tp->GetColor(ThemeProperties::COLOR_TOOLBAR));
 


But this is just a coincidence. I said old behavior because the CL is supposed to fix the old behavior.

I'm going to go ahead and revert so there's no urgency to find a fix. It should be easy to re-land the original change along with a fix.