When using content_shell to run tests, run them with '--single-process'

When using content_shell to run tests, run them with '--single-process'

It seems that the exit code of the renderer process is not correctly propagated
to content_shell (at least on windows). By passing the '--single-process' flag
to content_shell, we ensure that we can detect renderer crashes.

R=whesse@google.com

Committed: https://code.google.com/p/dart/source/detail?r=24840

[kustermann, 2013-07-09 12:20:09]

I expect that we need to do status file updates after this CL since a few tests
seem to be crashing.

[Bill Hesse, 2013-07-09 12:28:39]

lgtm

[kustermann, 2013-07-09 12:32:49]

thank you

[kustermann, 2013-07-09 12:33:27]

Committed patchset #1 manually as r24840 (presubmit successful).