RFR 8248273: Small clean up for PerfClassTraceTime

[Harold Seigel]

Hi,

Please review this small cleanup involving PerfClassTraceTime.

Open Webrev: 
http://cr.openjdk.java.net/~hseigel/bug_8248273/webrev/index.html

JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8248273

The fix was regression tested by running Mach5 tiers 1 and 2 tests and 
builds on Linux-x64, Linux-aarch64, Windows, and Mac OS X and by running 
Mach5 tiers 3-5 tests on Linux-x64.

Thanks, Harold