Code review request: three native memory tracking related bugs

[Zhengyu Gu]

7181989: NMT ON: Assertion failure when NMT checks thread's native
CR: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7181989
Webrev: http://cr.openjdk.java.net/~zgu/7181989/webrev.00/

We try to assert Thread's stack base to ensure that 
Thread::record_stack_base_and_size() to record native stack to NMT, but 
there is scenario that the thread fails to start, which no native stack 
is created and should not be asserted.

7181986: NMT ON: Assertion failure when running jdi 
ExpiredRequestDeletionTest
CR: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7181986
Webrev: http://cr.openjdk.java.net/~zgu/7181986/webrev.00/

This is a racing condition when C/C++ runtime exit handler is ran
before NMT worker thread exits. The exit handler calls _query_lock's
destructor while NMT worker thread is still holding it. The fix is to
make _query_lock a heap object, instead of static object, but the
drawback is that, it does not seem that _query_lock can be safely deleted.

Also, I reassigned MemSnaphot lock and query lock, so they participate 
in the deadlock detection logic.

7182543: NMT ON: Aggregate a few NMT related bugs
CRhttp://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7182543
Webrev: http://cr.openjdk.java.net/~zgu/7182543/webrev.00/

- Fixed generations_in_used calculation
- Wait MemRecorder instance count to drop to zero before completely 
shutdown NMT
- Added assertion for JavaThread in _thread_blocked state.


Thanks,

-Zhengyu