test runner needs to print exit codes

[peter-ahe-google]

Currently, we might see output like this:

2013-11-18 09:13:37.411 Warning: All tests passed, but exitCode != 0. (E:\b\build\slave\dartium-win-inc-be\build\src\build\Release\content_shell.exe --no-timeout --dump-render-tree http://127.0.0.1:49484/root_build/generated_tests/none-drt/tests_html_svgelement_test/test.html?crossOriginPort=49485&group=supported_animateTransform

I think it would be rather easy to print the value of exitCode.

[ricowind]

Set owner to @ricowind.
Removed Priority-Unassigned label.
Added Priority-Medium label.

[ricowind]

Fixed in revision 30401.

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Added Fixed label.