RFR (XS) CR 8015493: runtime/contended/OopMaps.java fails with OutOfMemory

[Aleksey Shipilev]

Hi,

This is the tiny fix for the nightly failure on the regression test:
  http://cr.openjdk.java.net/~shade/8015493/webrev.01/

Reasons:
  Due to the nature of test, R1 instance size is large (1880 bytes on
  my Linux x86_64), and we allocate 100K of them during the test. We
  do that in the test because we want to have some of the objects
  pushed through the garbage collection to catch unusual behavior.
  The flip side is, we have ~200 Mb heap allocated just for R1 objects.
  While it works nicely on some platforms, the default heap sizes
  may fail the test. This makes the issue the test bug.

Fix:
  Allocate 10K of R1 objects in the test, require -Xmx128m. The target
  heap occupancy for the test is then ~20Mb, so we have lots of
  headroom for all platforms.

Testing:
 (this falls into my definition of being trivial, so:)
 * jtreg: runtime/contended/ on Linux x86_64
 * manual testing with 8015270 partially reverted, OopMaps fails on
Linux x86_64, as would anyone expect for a good regression test
 * also looked through the code for other runtime/contended regression
tests, and those seem unaffected

Thanks,
-Aleksey.