I tricked myself into thinking that deadlock detection is off by default in TSan by looking at the default value of the detect_deadlocks flag and outdated docs. (Created a pull request to update docs.)
I even managed to confuse others: https://groups.google.com/forum/#!topic/thread-sanitizer/xYvnAYwtoDk
However, the default value is overwritten in code (TSan_flags.cc:InitializeFlags). The TSan/deadlock tests also rely on this
This changes aligns the default value of the flag with the actual default behavior.