[Mac] Move the reset of signal handlers to be very soon after the fork, befor...

[Mac] Move the reset of signal handlers to be very soon after the fork, before we do any mach IPC.

The MachPortSender constructor can sometimes hang forever (gets stuck in bootstrap_look_up()), so it is important to reset the child's signal handlers as early as possible.

Nico would like me to mention that this was his idea.

BUG=35374
TEST=If in the forever backwards spinner state, closing the tab should not quit the browser.
TEST=In general, renderers and extensions and plugins should still work.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=58558

[rohitrao (ping after 24h), 2010-09-03 19:57:34]

Mark and Adam: is this change scary?

The MachPortSender constructor can sometimes hang forever (gets stuck in
bootstrap_look_up), so it seems important to reset the child's signal handlers
as early as possible.  I've verified that resetting the handlers here prevents
the browser from getting a SIGTERM when you try to close a stuck tab.

[Mark Mentovai, 2010-09-03 20:15:23]

LGTM in any event. Not scary.

http://codereview.chromium.org/3302009/diff/3001/4001
File base/process_util_posix.cc (right):

http://codereview.chromium.org/3302009/diff/3001/4001#newcode541
base/process_util_posix.cc:541: RestoreDefaultExceptionHandler();
Hmm. I wonder if we should move this too.