[10] RFR: 8179040: Avoid Ticks::now calls when EventClassLoad is not enabled

[Claes Redestad]

Hi,

this patch removes calling Ticks::now when EventClassLoad isn't enabled, 
which
has an effect on class loading performance:

http://cr.openjdk.java.net/~redestad/8179040/hotspot.01/

When tracing isn't enabled trace/tracing.hpp has dummy implementations 
which
are easily optimized away by a compiler, which I've verified happens on 
linux
OpenJDK builds with tracing disabled.

On builds with tracing enabled then the changes means the call to get 
the time
only happen if the event is enabled, which achieves the sought after startup
optimization.

Thanks!

/Claes