RFR (XS) 8148813 - Windows os::check_heap needs more information

[Ioi Lam]

HI,

Please review a small Windows fix:

https://bugs.openjdk.java.net/browse/JDK-8148813
http://cr.openjdk.java.net/~iklam/jdk9/8148813_windows_check_heap.v01/

We have seen strange heap corruption fatal errors that produced mdmp
files (windows crash dumps),
e.g. https://bugs.openjdk.java.net/browse/JDK-8147481

However, when we load these mdmp files in WinDBG, "!heap -triage"
shows no heap corruption.

These are probably spurious errors reported by HeapWalk. To properly
diagnose such errors, this patch saves a few of the last seen
PROCESS_HEAP_ENTRY's into a ring buffer, which can later
be examined with a debugger.

Thanks
- Ioi