RFR(S) 8246019 PerfClassTraceTime slows down VM start-up

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8246019
http://cr.openjdk.java.net/~iklam/jdk16/8246019-avoid-PerfClassTraceTime.v01/

PerfClassTraceTime is (a rarely used feature) for measuring the time 
spent during class linking and initialization. However, it's quite 
expensive and it needs to start and stop a bunch of timers. With CDS, 
it's quite often for the overhead of the timer itself to be much more 
than the time it's trying to measure, giving unreliable measurement.

In this patch, when it's clear that the init and linking will be very 
quick, I disable the timer and count only the number of invocations. 
This shows a small improvement in start-up

Results of " perf stat -r 100 bin/java -Xshare:on 
-XX:SharedArchiveFile=jdk2.jsa -Xint -version "

59623970 59341935 (-282035)   -----  41.774  41.591 ( -0.183) -
59623495 59331646 (-291849)   -----  41.696  41.165 ( -0.531) --
59627148 59329526 (-297622)   -----  41.249  41.094 ( -0.155) -
59612439 59340760 (-271679)   ----   41.773  40.657 ( -1.116) -----
59626438 59335681 (-290757)   -----  41.683  40.901 ( -0.782) ----
59618436 59338953 (-279483)   -----  41.861  41.249 ( -0.612) ---
59608782 59340173 (-268609)   ----   41.198  41.508 (  0.310) +
59614612 59325177 (-289435)   -----  41.397  41.738 (  0.341) ++
59615905 59344006 (-271899)   ----   41.921  40.969 ( -0.952) ----
59635867 59333147 (-302720)   -----  41.491  40.836 ( -0.655) ---
================================================
59620708 59336100 (-284608)   -----  41.604  41.169 ( -0.434) --
instruction delta =      -284608    -0.4774%
time        delta =       -0.434 ms -1.0435%

The number of PerfClassTraceTime's used is reduced from 564 to 116 (so 
we have an overhead of about 715 instructions per use, yikes!).