RFR (S) 8218266: G1 crash in AccessInternal::PostRuntimeDispatch

[coleen.phillimore at oracle.com]

Summary: protection_domains can be unloaded in the dictionary pd_set.

Tested with test here: 
test/hotspot/jtreg/runtime/Dictionary/ProtectionDomainCacheTest.java and 
the test in the bug.  Also tested hs-tier1-3.

open webrev at http://cr.openjdk.java.net/~coleenp/2019/8218266.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8218266

Thanks,
Coleen