RFR: 8163353: NPE in ConcurrentHashMap.removeAll()

[Martin Buchholz]

Let's get in the fix for regression 8163353 quickly:
http://cr.openjdk.java.net/~martin/webrevs/openjdk9/jsr166-jdk9-integration/ConcurrentHashMap-keySet-removeAll/
https://bugs.openjdk.java.net/browse/JDK-8163353