GitLab

The thread watcher appears to be kicking on when we're trying to
remove a handle. Not sure why. This converts some DCHECKs to CHECKs
and fixes handling of the deadline. I suspect none of this will help,
but it's worth a shot.

BUG=399769
TEST=none
R=darin@chromium.org

Review URL: https://codereview.chromium.org/454433003

Cr-Commit-Position: refs/heads/master@{#288949}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288949 0039d316-1c4b-4281-b951-d872f2087c98