[reland] Do not block in SimpleThread::Start().
This CL is identical to https://codereview.chromium.org/2664953004.
The race condition that it highlighted in a TaskScheduler test the
first time that it landed was fixed by
https://codereview.chromium.org/2798373002/
There is no good reason to block in SimpleThread::Start().
In addition to introducing unnecessary latency, blocking in
Start() prevents a non-joinable DelegateSimpleThread from
being deleted from Run() without external synchronization
(it is wrong to delete SimpleThread while Start() is waiting
on the |event_| member).
BUG=
TBR=gab@chromium.org,jam@chromium.org,henrika@chromium.org
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Review-Url: https://codereview.chromium.org/2801073005
Cr-Commit-Position: refs/heads/master@{#462912}
CrOS-Libchrome-Original-Commit: d5acadb2d99dfbbde0cbe251173b566ceb5d3441
5 files changed