RFR: 8264166: OopStorage should support specifying MEMFLAGS for allocations

[Kim Barrett]

Please review this change to OopStorage to allow the MEMFLAGS value for associated allocations to be specified when the storage object is constructed.  This allows a subsystem that needs an OopStorage object to associate its allocation with others for that subsystem in NMT tracking and reporting.

Testing:
mach5 tier1.
Manually compared NMT output before and after this change for a test that generated a lot of one particular OopStorage entries.

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Commit messages:
 - add MEMFLAGS support to OopStorage

Changes: https://git.openjdk.java.net/jdk/pull/3188/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3188&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264166
  Stats: 64 lines in 16 files changed: 30 ins; 0 del; 34 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3188.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3188/head:pull/3188

PR: https://git.openjdk.java.net/jdk/pull/3188