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

util/mach/exception_ports.h

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 94 matching lines @@
 
   ~ExceptionPorts();
 
   //! \brief Calls `*_get_exception_ports()` on the target.
   //!
   //! \param[in] mask The exception mask, containing the `EXC_MASK_*` values to
   //!     be looked up and returned in \a handlers.
   //! \param[out] handlers The exception handlers registered for \a target_port
   //!     to handle exceptions indicated in \a mask. The caller must take
   //!     ownership of the \a port members of the returned ExceptionHandler
-  //!     objects. On failure, this argument is untouched.
+  //!     objects. If no execption port is registered for a bit in \a mask, \a
+  //!     handlers will not contain an entry corresponding to that bit. This is
+  //!     a departure from the `*_get_exception_ports()` functions, which may
+  //!     return a handler whose port is set to `EXCEPTION_PORT_NULL` in this
+  //!     case. On failure, this argument is untouched.
   //!
   //! \return `true` if `*_get_exception_ports()` returned `KERN_SUCCESS`, with
   //!     \a handlers set appropriately. `false` otherwise, with an appropriate
   //!     message logged.
   bool GetExceptionPorts(exception_mask_t mask,
                          std::vector<ExceptionHandler>* handlers) const;
 
   //! \brief Calls `*_set_exception_ports()` on the target.
   //!
   //! \param[in] mask A mask specifying the exception types to direct to \a
@@ skipping 47 matching lines @@
   // even with a MACH_PORT_NULL target_port, because it is incorrect to
   // deallocate the result of mach_task_self().
   bool dealloc_target_port_;
 
   DISALLOW_COPY_AND_ASSIGN(ExceptionPorts);
 };
 
 }  // namespace crashpad
 
 #endif  // CRASHPAD_UTIL_MACH_EXCEPTION_PORTS_H_