RFR (M): (7u60): Backport of 8027476: Improve performance of Stringtable unlink, 8027455: Improve symbol table scan times during gc pauses

[Thomas Schatzl]

Hi all,

  could I have reviews for the following backport of the symbol table/
string table parallelization change?

It implements parallelization of string table and symbol table scan
during G1 full GC and remark for 7u60.

There is some difference in the patches due to how 7u60 managing the
iteration over the string table:

- 7u60 has no StringTable/StringTable::unlink_or_oops_do() methods,
but only separate StringTable/SymbolTable::unlink() and
StringTable/SymbolTable::oops_do() methods.

- 7u60 allows sharing of strings using CDS, making minor changes
necessary

These differences are contained in symbolTable.?pp, the rest is
verbatim backport iirc.

New webrev:
http://cr.openjdk.java.net/~tschatzl/8027476/webrev

Old Webrev:
http://cr.openjdk.java.net/~tschatzl/8027476/webrev.1

CRs:
https://bugs.openjdk.java.net/browse/JDK-8027455
https://bugs.openjdk.java.net/browse/JDK-8027476

Testing:
jtreg test case, jprt, FMW apps

Thanks,
  Thomas