RFR: 8227559 JFR: Slow dump with path-to-gc-roots=true

[Erik Gahlin]

Hi,

Could I have a review of this fix. Most of the issues were fixed "8238592: JFR: Crash when dumping paths to gc roots on deep heaps” and this only adress a regression.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8227559 <https://bugs.openjdk.java.net/browse/JDK-8227559>

Webrev:
http://cr.openjdk.java.net/~egahlin/8227559/ <http://cr.openjdk.java.net/~egahlin/8227559/>

Testing: test/jdk/jdk/jfr 

Thanks
Erik