clock_get_monotonic - Acquire the current monotonic time.
#include <zircon/syscalls.h>
zx_time_t zx_clock_get_monotonic(void);
zx_clock_get_monotonic() returns the current time in the system
monotonic clock. This is the number of nanoseconds since the system was
powered on.
TODO(ZX-2399)
zx_clock_get() returns the current monotonic time.
zx_clock_get_monotonic() cannot fail.