RFR: 8216283,Allow shorter method sampling interval than 10 ms

[Erik Gahlin]

Hi,

Could I have a review of a fix that removes the 10 ms limit for the 
Method sampling event?

The .jfc-files are updated so instead of "Off", "Normal" and "Maximum," 
there will now be four alternatives  "Off", "Normal", "High" and "Very 
High", where "High" corresponds to "Maximum" (10 ms) and "Very High" is 
a sampling rate of 1 ms.

In benchmarks we see little impact on throughput if we use "1 ms", but a 
loss about 3% on max-jOPS on SpecJBB2015. This only happens if user 
opts-in on the "Very High" sampling rate.

The default intervals are still 20 ms for default.jfc and 10 ms for 
profile.jfc.

Webrev:
http://cr.openjdk.java.net/~egahlin/8216283/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8216283

Testing:
test/jdk/jdk/jfr/*

Thanks
Erik