Add NewMachPort() and its test, and switch call sites to use it

Add NewMachPort() and its test, and switch call sites to use it.

There were many call sites that wasted a few lines on
mach_port_allocate() and sticking the result into a scoper. I was about
to add three more, so I took the opportunity to simplify things.

TEST=util_test
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/a02f721637fc0c999f83796fe80044bc912fcc1a

[Mark Mentovai, 2014-12-17 18:51:35]

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

[Robert Sesek, 2014-12-17 20:06:47]

https://codereview.chromium.org/809103002/diff/1/util/mach/mach_extensions.cc
File util/mach/mach_extensions.cc (right):

https://codereview.chromium.org/809103002/diff/1/util/mach/mach_extensions.cc...
util/mach/mach_extensions.cc:32: mach_port_t port;
= MACH_PORT_NULL, and then you can just do MACH_LOG_IF and return port.

[Mark Mentovai, 2014-12-17 20:08:55]

Updated.

[Robert Sesek, 2014-12-17 20:09:21]

LGTM

[Mark Mentovai, 2014-12-17 20:10:42]

Committed patchset #2 (id:20001) manually as
a02f721637fc0c999f83796fe80044bc912fcc1a (presubmit successful).