RFR: 8205651: TestLargeRootSet fails with exception: Could not find root object

[Erik Gahlin]

Hi,

Could I have a review of a test that has failed intermittently. By 
increasing the size of the StackObject array the likelihood of the 
object sampler finding it increases.

I also added logging, so it is possible to see if the code path for a 
very large root set is taken. This is not the case, before or after the 
proposed change. It's hard to trigger that path. To start with, the heap 
must be at least 640 MB (32 MB/ 5%). I did however test with a modified 
JVM where the code path was triggered more easily and the test passed.

For now, I'm only making the test more stable and adding logging, so it 
easier to write a better test in the future.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8205651

Webrev:
http://cr.openjdk.java.net/~egahlin/8205651/

Thanks
Erik