RFR: JDK-8277520: Implement JDK-8 default methods for IdentityHashMap [v3]

[liach]

> Might need a CSR as now `computeIfAbsent` `computeIfPresent` `compute` `merge` would throw CME if the functions modified the map itself, and there are corresponding specification changes.

liach has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:

 - Merge branch 'identityhashmap-bench' into identityhashmap-default
 - Initial identity hash map benchmark
 - Merge branch 'master' of https://git.openjdk.java.net/jdk into identityhashmap-default
 - Merge branch 'master' of https://git.openjdk.java.net/jdk into identityhashmap-default
 - update dates
 - Also test cme for identity hash map
 - Fix putIfAbsent
 - JDK-8277520: Implement JDK-8 default methods for IdentityHashMap

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6532/files
  - new: https://git.openjdk.java.net/jdk/pull/6532/files/d853ab34..f6ee4fab

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6532&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6532&range=01-02

  Stats: 70198 lines in 2074 files changed: 48646 ins; 11878 del; 9674 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6532.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6532/head:pull/6532

PR: https://git.openjdk.java.net/jdk/pull/6532