Fix race in thread list destructor

The ThreadList::Contains wasn't being guarded by the thread list
lock, which could cause a corrupted thread list if another thread
unregistered itself while std::find was searching the thread list.

Bug: 17896374

(cherry picked from commit b90132cb5132eaeb4dbfca1e63d79b4005dacec5)

Change-Id: I8f6f979f365ca00ac0655e04eb26020d2ad7d6ee
1 file changed