[MessageLoop] Remove left behind TODO

Oops hadn't saved file locally before "git cl upload -c" for last patch
set @ https://chromium-review.googlesource.com/c/chromium/src/+/1153458

TBR=kylechar@chromium.org

Bug: None
Change-Id: I4466d287a80f4472b61da2017c28c01ff31c4dbb
Reviewed-on: https://chromium-review.googlesource.com/1155250
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: kylechar <kylechar@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579113}
1 file changed