RFR(XS): 8004170: G1: Verbose GC output is not getting flushed to log file using JDK 8

[John Cuthbertson]

Hi Everyone,

Can I have a couple of volunteers look over the changes for this CR - 
the webrev can be found at: 
http://cr.openjdk.java.net/~johnc/8004170/webrev.0/

Summary:
When we changed the G1 evacuation pause to not use instances of the 
TraceTime class we forgot to flush the GC log file (which happened 
during the TraceTime destructor). The fix is to add a flush call to 
G1CollectedHeap::log_gc_footer(). I also noticed that TraceCPUTime 
destructor does not flush the specified log file and, since it only 
seems to be instantiated from GC code, it probably should.

Testing:
GCOld with -XX:G1LogLevel=fine,finer,finest and -Xloggc. The submitter 
of the CR has also verified the fix.

Thanks,

JohnC