bionic_systrace.h contains an implementation of tracing that
can be used with systrace.py and its associated viewer. pthread_mutex
now uses this tracing to track pthread_mutex contention, which can be
enabled by using the "bionic" command line option to systrace.
Bug: 15116468
(cherry picked from commit a406ee6d5f616192e9a13afad6ac6a9969814fc1)
Change-Id: Ic98fc303689fe9384974150d0d258c50806a55e4