Chrome Version : 65.0.3284.0 (Official Build) 46c535d207b3648ddefdf3f9a588b69ac5ef31f2-refs/heads/master@{#521227} 64-bit
OS : Mac(10.12.6) (10.13.2)

Test URL : https://chrome.google.com/webstore/detail/cosmopolise/ipihgjdhjoldhpfpmiiimpnmohpfhkcm?utm_source=chrome-ntp-icon

What steps will reproduce the problem?
1. Launch chrome, open NTP, navigate to above test URL and apply ‘cosmopolise’ theme.
2. Open another NTP, go back to pervious tab (webstore) and click on ‘Undo’ button.
3. Observe the ‘X’ (close) icon for the NTP.

Actual Result : Tab’s ‘X’ (close) icon disappears after uninstalling a ‘cosmopolise’ theme.

Expected Result : Tab ‘X’ (close) icon should be visible even after uninstalling a ‘cosmopolise’ theme.

This is a regression issue broken in ‘M-58’ and using the per-revision bisect providing the bisect results,
Good build : 58.0.3000.0 (Revision : 447670)
Bad build : 58.0.3001.0 (Revision : 447896)

You are probably looking for a change made after 447825 (known good), but no later than 447826 (first known bad).

CHANGELOG URL:
https://chromium.googlesource.com/chromium/src/+log/28fbc2f08338a66ed15e96fd2841c66cbbda212f..524a361c86c23bb4f5384c1738f786532a296e46

Suspect : https://chromium.googlesource.com/chromium/src/+/524a361c86c23bb4f5384c1738f786532a296e46

@sdy : Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to concern owner.

Notes : 
1. ‘X’ (close) icon is visible only when hovering over a tab.
2. This is Mac OS specific issue and unable to reproducible it on Windows(7,8,10) & Linux(14.04 LTS) OS.
 

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