Note: 
Actual: Extra padding is also observed below done button.
Expected: Extra padding should not be seen below done button.

You are probably looking for a change made after 513360 (known good), but no later than 513361 (first known bad).
CHANGELOG URL:
The script might not always return single CL as suspect as some perf builds might get missing due to failure.
https://chromium.googlesource.com/chromium/src/+log/a28eb737c4c9424d7656ada19b688af854777968..1eca7aba022c190ea02e34dbd4ae52a8f5f88bbc

Suspecting: https://chromium.googlesource.com/chromium/src/+/1eca7aba022c190ea02e34dbd4ae52a8f5f88bbc
Could you please check whether this is caused with respect to your change, if not please help us in assigning it to the right owner.

Issue not seen on Mac & Linux OS.

Deleted: Actual_padding.png 105 KB

	Actual_padding.png 105 KB View Download

Below is the manual regression range
Good Build: 64.0.3256.0 
Bad Build:  64.0.3257.0 

I think these are all expected changes. In the 'expected' screenshot, the buttons are already cramped with the French strings. When the width of the "OK" button matches widths, the dialog width exceeds the threshold for the minimum size and snaps to the next standard dialog width.

The the "sign in to Chrome" link is configured not to split across lines, but it doesn't fit on the first line, and so wraps on to the second.

Agreed, this looks expected to me too.