Add a UseCounter for nested workers

Bug: 31666
Change-Id: If63450bf5fdae8a32ef5d8bf0c79fa1f28a52f38
Reviewed-on: https://chromium-review.googlesource.com/1130107
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Nate Chapin <japhet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573747}
3 files changed