Fix VM exit code in some cases.

Fix VM exit code in some cases.

R=asiva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=27926

[siva, 2013-09-26 00:38:29]

lgtm

[regis, 2013-09-26 01:10:51]

Committed patchset #1 manually as r27926 (presubmit successful).

[kustermann, 2013-09-26 09:35:39]

Awesome, thank you.