8162795: RFR: [REDO] MemberNameTable doesn't purge stale entries

[Kevin Walls]

Hi,

This is a review request for:
[REDO] MemberNameTable doesn't purge stale entries
https://bugs.openjdk.java.net/browse/JDK-8162795

For certain apps, such as those with heavy use of the JavaScript engine, 
the MemberNameTable and its weak references can introduce considerable 
GC overhead.  In some cases GC cannot keep up with the activity and 
collection times continually increase.  This is a regression in jdk8 or 
later, compared to e.g. jdk7.

The change in 8152271:
https://bugs.openjdk.java.net/browse/JDK-8152271
MemberNameTable doesn't purge stale entries

...fixes this, but that was reverted from 9 due to a regression in a 
microbenchmark.  While that benchmark is a concern, more serious is the 
regression currently out there for certain apps when moving up to JDK 8 
or 9.  Adding back the change in 8152271 fixes this.

Re-applying the original change from 8152271 by Coleen still works, with 
one copyright date fixup.  A webrev is:

http://cr.openjdk.java.net/~kevinw/8162795/webrev.00/

Plan is to re-integrate the 8152271 change in 9 (this request), and 
backport to 8.  Meanwhile, a better solution for MemberNameTable in 
jdk10 is being pursued in https://bugs.openjdk.java.net/browse/JDK-8174749

Thanks
Kevin