RFR(XS): 8198585: add asserts to verify that ServiceUtil::visible_oop is not needed

[Chris Plummer]

Hello,

Please review the following:

https://bugs.openjdk.java.net/browse/JDK-8198585
http://cr.openjdk.java.net/~cjplummer/8198585/webrev.00/webrev/

Before removing ServiceUtil::visible_oop(), I want to make sure it 
really isn't needed. Supposedly it should never return false, thus 
negating the need for its existence. This change adds asserts whenever 
false is returned. If it makes it all the way through promotion testing, 
then I'll delete the ServiceUtil::visible_oop() code and the references 
to it.

I tested by running all jdk and hotspot tier1-3 tests.

thanks,

Chris