GitLab

Once Signal()ed, OneShotEvent should drop all the references to
the tasks, otherwise OneShotEvent::tasks_ would continue to hold
references to users of OneShotEvent::Post(), for the lifetime
of OneShotEvent.

This CL clears |tasks_| once Signal() is called, dropping those
references correctly. In future, OneShotEvent::Post() will take
OnceClosure instead of (repeating) Closure.

This CL also adds a regression test for the same.

Bug: 853649
Change-Id: I10270318ff8393a9af0b8da299a1866df936b273
Reviewed-on: https://chromium-review.googlesource.com/1103606
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568184}