10 RFR: WhiteBox methods should throw an exception if used with inappropriate collector.

[Michail Chernov]

Hi,

Could I have a reviews for this change, please?

Whitebox.cpp has many methods which can cause to VM assertion failure 
when they are used with inappropriate collector. For example - 
WB_G1IsHumongous, WB_G1NumFreeRegions, etc.
There also several methods which throw RuntimeException when methods are 
used with wrong collector (WB_PSHeapGenerationAlignment, 
WB_PSVirtualSpaceAlignment).

This change adds checking of collector which is used and throwing 
RuntimeException when the method is used with wrong collector.

http://cr.openjdk.java.net/~mchernov/8167196/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8167196

The change was tested - all gc tests pass with this change with 
different collectors.

Thanks,
Michail