mac: Add CrashpadClient::UseSystemDefaultHandler()

mac: Add CrashpadClient::UseSystemDefaultHandler()

Chrome’s relauncher process needs a way to sever ties with the
crashpad_handler instance running from the disk image in order to cause
that instance to exit so that the disk image may be unmounted. This new
function is otherwise not thought to be interesting, and its use is not
recommended.

This comes with a small refactoring to create a
SystemCrashReporterHandler() function, and a fix for a minor port leak
in CrashReportExceptionHandler::CatchMachException().

BUG=chromium:538373
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/cd85c9f700f7efda7ffa36e0017806a2263f4d08

[Mark Mentovai, 2015-10-02 18:24:06]

mark@chromium.org changed reviewers:
+ rsesek@chromium.org

[Robert Sesek, 2015-10-02 18:30:19]

https://codereview.chromium.org/1375573005/diff/1/util/mach/mach_extensions.h
File util/mach/mach_extensions.h (right):

https://codereview.chromium.org/1375573005/diff/1/util/mach/mach_extensions.h...
util/mach/mach_extensions.h:130: exception_handler_t
SystemCrashReporterHandler();
I think this could return a ScopedMachSendRight, since ScopedGeneric now has
move support.

[Mark Mentovai, 2015-10-02 18:38:21]

I forgot that was based on ScopedGeneric. Updated.

[Robert Sesek, 2015-10-02 18:39:11]

LGTM

[Mark Mentovai, 2015-10-02 18:41:07]

Committed patchset #2 (id:20001) manually as
cd85c9f700f7efda7ffa36e0017806a2263f4d08 (presubmit successful).