MachMessageServer: Make request messages const

MachMessageServer: Make request messages const.

There’s no reason that “in” or “request” messages should be non-const.
This makes them const, bridges the const gap left by the MIG-generated
“check” functions with wrappers, and uses non-const fields in
“out” messages instead of const fields in “in” messages for in-out
parameters.

TEST=util_test ExcServerVariants.*:MachMessageServer.*
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/fbf12950fe7f2be016eed387c6be660901e5e546

[Mark Mentovai, 2014-09-10 21:54:59]

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

[Robert Sesek, 2014-09-10 21:56:45]

https://codereview.chromium.org/564533002/diff/1/util/mach/exc_server_variant...
File util/mach/exc_server_variants.cc (right):

https://codereview.chromium.org/564533002/diff/1/util/mach/exc_server_variant...
util/mach/exc_server_variants.cc:146: // The MIG-generated
__MIG_check__Request__*() functions are not declared as
Could you do this in the mig.py script instead, and just fix the generated code?

[Mark Mentovai, 2014-09-10 22:35:01]

https://codereview.chromium.org/564533002/diff/1/util/mach/exc_server_variant...
File util/mach/exc_server_variants.cc (right):

https://codereview.chromium.org/564533002/diff/1/util/mach/exc_server_variant...
util/mach/exc_server_variants.cc:146: // The MIG-generated
__MIG_check__Request__*() functions are not declared as
rsesek wrote:
> Could you do this in the mig.py script instead, and just fix the generated
code?

That’s substantially harder. It’s pretty easy to fix the declaration in the
header and the prototype where it’s defined, but it winds up triggering problems
at call sites in the implementation file, because you can’t implicitly convert a
Request** to a const Request**. Rewriting those call sites to have casts too is
a lot trickier.

The exact problem is http://c-faq.com/ansi/constmismatch.html.

[Robert Sesek, 2014-09-10 22:42:30]

OK LGTM

[Mark Mentovai, 2014-09-10 22:57:21]

Committed patchset #1 (id:1) manually as fbf1295 (presubmit successful).