[master] RFR: Simplify stable_mark() routine

[Roman Kennke]

The code in ObjectSynchronizer::stable_mark() is a bit over-complicated: it has a 'fast' path (which really isn't a fast-path, because the really-fast path is already in the various oopDesc::klass() methods), and for the slow-path loop dives into ObjectSynchronizer::safe_load_mark(). This change proposes to remove the stable_mark() method, and rename safe_load_mark() to stable_mark() instead.

I also propose a small improvement: we can use read_stable_mark() to deal with INFLATING mark properly, and handle the remaining cases in the loop: monitor and stack-locked are the most common - deal with them first. Stack-locked can safely access the mark when current thread is owning thread of the lock - avoid CASing INFLATING into the header in this case. Neutral and Marked cases go last, because they should not be very common (neutral is already caught in oopDesc::klass() variants, marked should only happen during full GCs by GC internal code).

Testing:
 - [x] tier1
 - [ ] tier2
 - [ ] tier3
 - [ ] tier4

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Commit messages:
 - Simplify stable_mark() routine

Changes: https://git.openjdk.java.net/lilliput/pull/46/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lilliput&pr=46&range=00
  Stats: 61 lines in 3 files changed: 12 ins; 42 del; 7 mod
  Patch: https://git.openjdk.java.net/lilliput/pull/46.diff
  Fetch: git fetch https://git.openjdk.java.net/lilliput pull/46/head:pull/46

PR: https://git.openjdk.java.net/lilliput/pull/46