Add code to the worker to fool isolate_helper into thinking it isn't the result of spawning an isol…

Add code to the worker to fool isolate_helper into thinking it isn't the result of spawning an isolate.

R=kasperl@google.com

Committed: https://code.google.com/p/dart/source/detail?r=31744

[ahe, 2014-01-09 20:40:58]

According to my test plan, it is premature to start work on an automated test
suite for this kind of regression/bug.

So I added a file with a comment that will help me remember how to manually test
it. Eventually, this will help me design the automated test framework.

[kasperl, 2014-01-10 07:26:01]

LGTM.

[ahe, 2014-01-13 16:07:10]

Committed patchset #1 manually as r31744 (presubmit successful).