You are probably looking for a change made after 553261 (known good), but no later than 553262 (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/2e19e404fbd1e6e900fbe953eb5f4416f3136b2d..3a1317cc430d455c7ba83c3e14c4e6ff45381f51

Suspect: https://chromium.googlesource.com/chromium/src/+/3a1317cc430d455c7ba83c3e14c4e6ff45381f51

@edwardjung: 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.

I made the switch to the white UI, the close X is added from another place and would need to be adjusted so that there is enough colour contrast. I suspect the X is there but not visible. I would argue that there wasn't enough contrast in the old version either.

Someone from the desktop identity team would need to look at this. 

@bklmn do you know the identity engineers to assign this bug to. 

edwardjung@chromium.org: This icon is defined at https://cs.chromium.org/chromium/src/chrome/browser/resources/inline_login/inline_login.html?rcl=ab1fe7b88d94d8a5303226a0d95a9c8a70a46df9&l=26 

We (the sign-in team) own it, however we are not experts on webUI stuff. If you know WebUI, would you mind taking a look as your CL added the regression? Also, from a UX perspective, what color should this button be?

Yeah this would be the identity team..Im glad to help however. 

cjacqueline@ was the UXer we were working with on the DICE/Unity work. 

Assigned to achuith, who is the owner of that folder. 

@achuith could you update the colour of the close X button. It's not visible on a white error interstitial.

@bklmn, could you give the standard colour value that would work for a white background error state in a dialog?

I'm on the chromeos team; Elias might be able to find an appropriate owner for this.

I think we need two things:
- Clear definition from UX (bklmn/bettes) on what the color value for the "x" should be. Alan and Joel, for reference: this is the "x" in the top-left corner of the modal sign-in dialogue that shows up when you click a "Sign into Chrome" promo pre-Dice.
- Eng ownership to update the color of the button

Let's figure out the color first (assigning to Joel). Note that this will become obsolete once we roll out Dice to 100%, but there's a small chance that won't happen by 68 (at least it may not be on by default), so we should fix this until that happens.

Lowering priority though, since Dice will make this essentially obsolete.

--Chrome Identity automated triaging--

This bug is Untriaged and has gone for two weeks without any activity, so it is being moved to Available. Please see https://goo.gl/78kbny for more details. Please remove the Services>SignIn or UI>Browser>Profiles components if this bug isn't related to Chrome Identity.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

--Chrome Identity automated triaging--

This bug is Assigned and has gone one month without any activity, so it is being moved to Available to indicate that it is not actively being worked on. If you are working on this bug, please mark yourself as the owner and move back to Assigned. Please see https://goo.gl/78kbny for more details. Please remove the Services>SignIn or UI>Browser>Profiles components if this bug isn't related to Chrome Identity.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Obsolete with Dice.