RFR(M) : 8059624 : Test task: WhiteBox API for testing segmented codecache feature

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev/8059624/webrev.00/
660 lines changed: 624 ins; 2 del; 34 mod;

Hi all,

please review the patch which adds new WhiteBox methods needed for 
better testing SegmentedCodeCache:
  - perform allocation in code cache
  - force code cache sweep
  - lock/unlock compilation
  - get a segment id for nmethod.
besides these methods, the patch also adds a method to get all entries 
in code heap.

changes in product code:
  - monitor 'Compilation_lock' was added to implement compilation 
locking/unlocking
  - align_code_offset function was made a static member of CodeBlob
  - WhiteBox was made a friend of several classes

testing: jprt, new added tests
jbs: https://bugs.openjdk.java.net/browse/JDK-8059624

-- 
Thanks,
Igor