Tabs grow too large or small when closing, until mouseout

[petemill]

Test plan

#11436 (comment)

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Description

When using the mouse to close tabs via the close button [x], all the tabs often grow larger than the tab should be, not only making the next tab's close button not under the mouse cursor, but making all the tabs either too large or too small compared to how they will end up when the mouse is moved away from the tabs

Steps to Reproduce

1. Make the window narrow
2. Open ~7 tabs (enough for the tabs to fill the width of the container and get smaller
3. Mouse over the first tab's close button and click it

Actual result:
The next tab grows bigger (or smaller if you opened many many tabs)

Expected result:

The next tab stays exactly the same size, until mouseout of the tab bar

Brave Version

master - 74688c9 (0.21.0)
macOS

Reproducible on current live release:
No, neither on 0.19.37