I think this will make a rtc::Thread object exist for the lifetime of
the environment, which will remove some uninteresting crashes.
BUG=chrome:648075
Review-Url: https://codereview.webrtc.org/2365373002
Cr-Commit-Position: refs/heads/master@{#14438}
found chromium:620694.
Unfortunately it depends on unsafe GN targets, so do not build in
Chromium.
NOTRY=true
Review-Url: https://codereview.webrtc.org/2129603003
Cr-Commit-Position: refs/heads/master@{#13407}