RFR (S) Urgent: 8221208: Backout JDK-8218446

[David Holmes]

Bug: https://bugs.openjdk.java.net/browse/JDK-8221208
webrev: http://cr.openjdk.java.net/~dholmes/8221208/webrev/
Original changeset: http://hg.openjdk.java.net/jdk/jdk/raw-rev/d9f43dfbe524

The fix for JDK-8218446 is flawed and can lead to crashes - see:

https://bugs.openjdk.java.net/browse/JDK-8221207

I understand what needs to be changed but it will take time to verify 
the details, so backing this out before it causes testing problems.

Thanks,
David