RFR: JDK-8303605: Memory leaks in Metaspace gtests [v4]

[Justin King]

> Fix memory leaks identified while running Metaspace gtests.

Justin King has updated the pull request incrementally with one additional commit since the last revision:

  Switch to C-style cast
  
  Signed-off-by: Justin King <jcking at google.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12865/files
  - new: https://git.openjdk.org/jdk/pull/12865/files/57df305e..5b368b60

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12865&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12865&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12865.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12865/head:pull/12865

PR: https://git.openjdk.org/jdk/pull/12865