mac: Scope crashpad_handler’s SIGTERM handler more broadly

mac: Scope crashpad_handler’s SIGTERM handler more broadly

Previously, there was a window after starting the upload thread but
before the SIGTERM handler was installed, where receipt of SIGTERM
could have interrupted an in-progress upload. There was also the
possibility that a second SIGTERM sent after the exception handler
stopped running would interrupt an in-progress upload. By pulling the
signal handler out of ExceptionHandlerServer and into the main
function, these races are avoided.

BUG=crashpad:25
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/crashpad/crashpad/+/4a7d599b6494c1b76208b7136c0a8dde5d2838c1

[Mark Mentovai, 2015-11-06 17:14:43]

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

[Robert Sesek, 2015-11-09 21:19:57]

LGTM

[Mark Mentovai, 2015-11-09 21:29:29]

Committed patchset #2 (id:20001) manually as
4a7d599b6494c1b76208b7136c0a8dde5d2838c1 (presubmit successful).