Functional:
  - eosterlund v2.10 CR: reorganize deflate_monitor_using_JT() to use
    "early exit" style
  - dcubed - clarify/fix/rearrange a few comments in deflate_monitor_using_JT()
  - eosterlund v2.10 CR: simplify install_displaced_markword_in_object()
  - dcubed - save_om_ptr()'s call (now ObjectMonitor::enter()'s call) to
    install_displaced_markword_in_object() can race with the deflater
    thread's clearing of the object field so handle that with a local
    copy of the oop.
  - dcubed - DaCapo-h2 perf testing showed that ref_counting causes a
    ~22.8% slow down with -XX:-AsyncDeflateIdleMonitors ("off" mode).
    The slow down with "on" mode -XX:+AsyncDeflateIdleMonitors is ~17%.
    Removed ObjectMonitor::_ref_count, the associated functions and the
    ObjectMonitorHandle class. Updated all the previous ObjectMonitorHandle
    sites with a comment explaining the interaction with async monitor
    deflation at that point. The second part of the async deflation protocol
    moves from the _ref_count field to the _contentions field (which is how
    Carsten did it in his prototype).
  - Migrated the ObjectMonitor::_contentions field away from volatile to
    using Atomic operations.

Test update:
  - None.

Cleanup:
  - Clarify comments in BasicLock::move_to() and
    SharedRuntime::OSR_migration_begin(); most of these changes are
    baseline related so they could be pushed with a separate sub-task.

Notes:
  - src/hotspot/share/runtime/thread.hpp in the "full" webrev has no
    changes. The "inc" webrev shows the changes that were removed by
    the v2.11 patch.

  - src/hotspot/share/services/threadService.cpp has an include for
    runtime/safepointVerifiers.hpp that was added for an earlier
    version of v2.11. It's no longer needed so I'll be removing that
    before I push.