When forking, restore the default exception handler port....

When forking, restore the default exception handler port.

The browser process launches children with fork && exec.  On the Mac, this
results in a child that has its exception ports set the same as the parent.
When Breakpad is enabled, this means that a child such as a renderer process
begins its life with its exception port pointing to a Breakpad instance
running inside the browser.  This is not intended.  Even if the child installs
its own Breakpad handler (which a renderer would), the previous handler would
be pointing to the instance inside the browser, and if the child's Breakpad
is misconfigured to pass exceptions to the previous handler it will wind up
being passed back to the parent.  The misconfiguration was corrected in r25311.
This change restores the default exception handler port, which should be
Apple Crash Reporter/ReportCrash, in the child process immediately after it
it has been forked.

BUG=20371
TEST=None, because r25311 fixed the visible aspect of this bug

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=25371

[Mark Mentovai, 2009-09-03 19:56:03]

In a Breakpad-enabled release build with this change, renderer crashes go to
Breakpad but not Apple Crash Reporter.  Browser crashes go to Breakpad and then
to Apple Crash Reporter.

I will test the behavior with a non-Breakpad-enabled debug build.

[Mark Mentovai, 2009-09-03 20:05:54]

Breakpad-enabled release build with this change: browser crashes go to Breakpad
and then to Apple Crash Reporter, renderer crashes go to Breakpad but not Apple
Crash Reporter.

Breakpad consent removed from that build: browser crashes go only to Apple Crash
Reporter, renderer crashes go nowhere.

Ordinary debug build with this change: browser crashes and renderer crashes both
go nowhere.

[jeremy, 2009-09-03 20:33:28]

LGTM!!

Please test on 10.6 before submitting.

http://codereview.chromium.org/200007/diff/1/4
File base/process_util.h (right):

http://codereview.chromium.org/200007/diff/1/4#newcode423
Line 423: // in the child after forking will restore the standard exception
handler.
Could you please add a link to the bug to fill out the documentation here a bit.

[Mark Mentovai, 2009-09-03 21:06:19]

I've added a link to the bug.

The behavior is the same on 10.5 and 10.6.

[jeremy, 2009-09-03 21:25:42]

Still LGTM