RR(XS): 7154963 crash in JvmtiEnvBase::get_current_contended_monitor()

[Sergey Gabdurakhmanov]

Hello,

Here is webrev of changes I'm about to integrate:

webrev: http://cr.openjdk.java.net/~sgabdura/7154963/webrev.00/
bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7154963

The fix check that the _java_thread parameter is valid when it is 
possible that the JavaThread has exited after the initial checks were 
made in generated/jvmtifiles/jvmtiEnter.cpp: 
jvmti_GetCurrentContendedMonitor().

The fix checked by customer on JDK6. Crash is not reproducible with this 
fix.

BR,
Sergey