[d8] Fix flakiness when calling quit() with isolates

[d8] Fix flakiness when calling quit() with isolates

Don't use exit(), use Shell::Exit() (which calls _exit() instead). This won't
run C++ static destructors, atexit() functions, etc., which can occasionally
cause flaky failures.

BUG=v8:4279
R=machenbach@chromium.org
LOG=n

Committed: https://crrev.com/41fa3573d53d0d1b45a3c08ef1cb53535dec4bf2
Cr-Commit-Position: refs/heads/master@{#30229}

[binji, 2015-08-17 22:18:56]

I tested this with:
tools/run-tests.py --buildbot --outdir out --arch x64 --mode Debug --isolates
mjsunit/regress/regress-4279 --stress-only --random-seed-stress-count=10000

[Jarin, 2015-08-18 05:03:44]

jarin@chromium.org changed reviewers:
+ jarin@chromium.org

[Jarin, 2015-08-18 05:03:44]

lgtm

[binji, 2015-08-18 16:46:05]

The CQ bit was checked by binji@chromium.org

[commit-bot: I haz the power, 2015-08-18 16:46:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1294913005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1294913005/1

[commit-bot: I haz the power, 2015-08-18 16:47:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-18 16:47:44]

Patchset 1 (id:??) landed as
https://crrev.com/41fa3573d53d0d1b45a3c08ef1cb53535dec4bf2
Cr-Commit-Position: refs/heads/master@{#30229}