RFR: Assert code roots are to-space ptrs when scanning/updating other roots

[Aleksey Shipilev]

On 02/13/2017 04:48 PM, Roman Kennke wrote:
> Instead of not scanning code roots at all when we don't have to, we
> could check that all the oops in them actually point to to-space
> objects as we're expecting. Implemented like this:
> 
> http://cr.openjdk.java.net/~rkennke/assertcoderoots/webrev.00/

OK. The indenting is inconsistent in ShenandoahUpdateRootsTask, but otherwise
looks good.

Thanks,
-Aleksey