Not sure about Chrome, but here's the bug for adding it to Webkit:

https://bugs.webkit.org/show_bug.cgi?id=92769

It's marked as RESOLVED FIXED, but I honestly can't tell from the comments if it was ever actually merged in.

There's also an initiative to begin using it in Firefox's built-in dev tools, still in-progress:

https://bugzilla.mozilla.org/show_bug.cgi?id=816756

(By the way, the difference in readability between the old and new Bugzilla is startling. Good job, Bugzilla team.)