Add assertion to check that CPU profiling actually works.

Recently I tried to debug CPU profiling on Chrome.

I've found that profiling is not working in Debug version.
The actual problem is that sandbox/playgroung configuration is wrong and tgkill syscalls are disallowed.

This patch will make such cases more clear.

Committed: http://code.google.com/p/v8/source/detail?r=13411

[Jakob Kummerow, 2013-01-17 13:46:12]

LGTM, landing.

I'm not quite convinced that crashing by means of a failing ASSERT is the best
reaction when requesting a profiling tick fails (as opposed to, say, printing a
warning); but we can always change that if this behavior turns out to be
annoying.

[caseq1, 2013-01-17 13:56:28]

On 2013/01/17 13:46:12, Jakob wrote:

> I'm not quite convinced that crashing by means of a failing ASSERT is the best
> reaction when requesting a profiling tick fails (as opposed to, say, printing
a
> warning); but we can always change that if this behavior turns out to be
> annoying.

Well, judging by possible result codes in tgkill(2), it can only fail if either
argument is invalid or we don't have permission. Either case seems like a
fundamental violation of our expectations, so I think it justifies the assert.