I'm trying to track it down to a specific revision, but it doesn't look like it corresponds to a WebKit or Chrome rev.
last known good win webkit build: chrome r165045 wk r132885
last known good win webkit build: chrome r165056 wk r132955
first known bad win webkit build: chrome r165062 wk r132891
first known bad win webkit build: chrome r165065 wk r132965
first known bad win webkit build: chrome r164894 wk r132893
(Note that this is an agglomeration of DEPS and canary results, so it's a bit confusing).
So it looks like one bot failed at Chrome 164895, but another bot passed at 165045.
One bot failed at WebKit r132891, but another bot passed at 132955.
So I don't think it's a WebKit or Chrome change.
(And once a bot starts hanging, it continues hanging after a reboot, so it's not a flakiness problem AFAICT).
Stephen