exc_server_variants: Templatize and use CompositeMachMessageServer

exc_server_variants: Templatize and use CompositeMachMessageServer.

The implementations for the exc and mach_exc subsystems were nearly
identical, and were a good target for templatization. The existing
split between exc and mach_exc was a good candidate for unification
based on CompositeMachMessageServer instead of the custom unification
previously done in UniversalMachMessageServer.

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

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/508a33dc7ae7da99abbc5cf4756c872388b9fea6

[Mark Mentovai, 2014-12-04 23:19:49]

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

[Mark Mentovai, 2014-12-04 23:19:49]

This is a net reduction of 448 lines!

[Robert Sesek, 2014-12-11 16:32:28]

LGTM

https://codereview.chromium.org/766193006/diff/20001/util/mach/exc_server_var...
File util/mach/exc_server_variants.h (right):

https://codereview.chromium.org/766193006/diff/20001/util/mach/exc_server_var...
util/mach/exc_server_variants.h:116: // Pointer-to-implementation (pimpl). The
implementation relies on internal
Not sure this comment is even necessary.

[Mark Mentovai, 2014-12-11 19:29:46]

Committed patchset #3 (id:40001) manually as
508a33dc7ae7da99abbc5cf4756c872388b9fea6 (presubmit successful).