UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.117 Safari/537.36

Example URL:
see attached HTML file

Steps to reproduce the problem:
1. Open the attached HTML file (chrome-crash.html) in a Chrome tab
2. Click on "click here", or otherwise add the "clicked" class to the ".clickable" div (eg in the Inspector)

What is the expected behavior?
The :before gets rotated 90 degrees, per the CSS rule.

What went wrong?
1. The tab appears to hang and doesn't respond to clicks etc.
2. After a while the "wait or exit" dialog appears
3. Looking at the tab's process in the Chrome Task Manager shows that the tab pegs the CPU to 100 and its memory usage goes through the roof.

Does it occur on multiple sites: Yes

Is it a problem with a plugin? No 

Did this work before? Yes Previous release in the Stable channel (ie Chrome 65)

Does this work in other browsers? Yes

Chrome version: 66.0.3359.117  Channel: stable
OS Version: OS X 10.13.4
Flash Version: 

Reproduced on multiple machines in multiple OSes (both OSX and Windows).

I observed this bug in the wild (ie, on a page on the site I develop). The enclosed HTML is the result of my attempts to minimise the amount of markup required to reproduce the bug. I expect it probably isn't a fully minimal repro, but I did my best; the attached HTML represents the point at which everything I tried to remove caused the bug to go away.

I attempted to collect a crash log, per the instructions in the wiki, but I couldn't seem to make it write out the file upon killing the process. I can provide a core dump if necessary. (Too big to upload in this form.)
 

Deleted: chrome-crash.html 794 bytes

chrome-crash.html 794 bytes View Download