Linux Sandbox: check no threads before fork().

Always check that no threads are running before fork().

BUG=327241
NOTRY=true

Review URL: https://codereview.chromium.org/108173008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239894 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed