Fix: test-debug.cc: don't misuse C++.

Fix: test-debug.cc: don't misuse C++.

The test in question (test-debug/LiveEditEnabled) is expected to fail, and it
failed, but because of the wrong reason (the test asserts that the default
isolate is not initialized, SetLiveEditEnabled initialized the default
isolate because it doesn't get one as param). Now it fails because of the right
reason.

R=ulan@chromium.org
BUG=

Review URL: https://codereview.chromium.org/99043004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18203 ce2b1a6d-e550-0410-aec6-3dcde31c8c00