Restart crashpad_handler on Mac if it exits unexpectedly

Restart crashpad_handler on Mac if it exits unexpectedly

This feature is only operative on OS X 10.10 and later, as directed by
CrashpadClient::StartHandler(). This limitation is enforced because the
handler restarter can cause the browser process to become an unreapable
pseudo-zombie on earlier OS versions if it crashes while a handler
restart is pending.

Committed: https://crrev.com/2c777f1149c46c47eaa3307a38070c82eff93835
Cr-Commit-Position: refs/heads/master@{#361201}

[Mark Mentovai, 2015-11-23 21:43:38]

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

[Robert Sesek, 2015-11-23 21:51:25]

LGTM

[Mark Mentovai, 2015-11-23 21:53:09]

The CQ bit was checked by mark@chromium.org

[commit-bot: I haz the power, 2015-11-23 21:55:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1470073002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1470073002/1

[commit-bot: I haz the power, 2015-11-23 22:24:55]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-23 22:25:46]

Patchset 1 (id:??) landed as
https://crrev.com/2c777f1149c46c47eaa3307a38070c82eff93835
Cr-Commit-Position: refs/heads/master@{#361201}