review request for CR 6361589

[Yumin Qi]

Fixed 6361589: Print out stack trace for target thread of GC crash

http://cr.openjdk.java.net/~minqi/6361589

Comments: This is a facility to assist for JVM crash analysis. To 
implement this function, it needs record JavaThread which may involve 
crash somewhere in GC thread. The place chosen here is NamedThread from 
which all GC threads but VMThread derive. I change VMThread's base from 
Thread to NamedThread, so the recording of JavaThread covers for GC 
threads and VMThread. Once the JavaThread recorded in GC thread seen 
during error report, its stack trace be printed out. To test this 
function, add a debug flag CrashGCForDumpingJavaThread, once it is set, 
it will crash immediately in VMThread or GC Thread to core dump. Note 
this is for test only purpose, no defects in involved JavaThread.


Thanks
Yumin