RFR(xs): 8199656: Make slow metaspace verifications switchable in debug builds

[Thomas Stüfe]

Hi all,

may I please have reviews for this small rfe:

Bug: https://bugs.openjdk.java.net/browse/JDK-8199656
webrev:
http://cr.openjdk.java.net/~stuefe/webrevs/8199656-verifymetaspace-switch/webrev.00/webrev/

We have a number of useful metaspace verifications which are all switched
off via a const bool in code. This change makes these verifications
switchable.

Note: the switch is develop because all the verifications are ASSERT only,
so it makes no sense to make it the switch diagnostic. If we want the tests
in product builds too, we need to revise the test code.

For the effect this has,
try ./hotspot/variant-server/libjvm/gtest/gtestLauncher.exe
-XX:-VerifyMetaspace -jdk:./images/jdk/
--gtest_filter=MetaspaceAllocationTest*. With verifications, runtime almost
triples in fastdebug.

Thanks and Kind Regards, Thomas