ExceptionPorts test: accept a port of MACH_PORT_NULL as “no handler.”

util/mach/exception_ports.h

Index: util/mach/exception_ports.h
diff --git a/util/mach/exception_ports.h b/util/mach/exception_ports.h
index 2592d74b55548856d504282d92fe8084eb2ecaef..6b509331a3edb69d6e4cd37b75c58082ba9fa746 100644
--- a/util/mach/exception_ports.h
+++ b/util/mach/exception_ports.h
@@ -117,6 +117,13 @@ class ExceptionPorts {
   //! \return `true` if `*_get_exception_ports()` returned `KERN_SUCCESS`, with
   //!     \a handlers set appropriately. `false` otherwise, with an appropriate
   //!     message logged.
+  //!
+  //! \note One element at most will be returned in \a handlers for each bit set
+  //!     in \a mask. If no exception port is registered for a bit in \a mask,
+  //!     there will either be no entry corresponding to that bit in \a
+  //!     handlers, or there will be an entry whose ExceptionHandler::port field
+  //!     is set to `MACH_PORT_NULL`. The precise behavior depends on the

[Robert Sesek, 2014/09/22 15:08:23]

Would it not be better to have ExceptionPorts normalize the behavior?

+  //!     underlying operating system and the target type.
   bool GetExceptionPorts(exception_mask_t mask,
                          std::vector<ExceptionHandler>* handlers) const;