RFR: 8276337: Use override specifier in HeapDumper [v2]

[Leo Korinth]

> Use override specifier in HeapDumper. It is safer.

Leo Korinth has updated the pull request incrementally with one additional commit since the last revision:

  restart failed github tests

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6274/files
  - new: https://git.openjdk.java.net/jdk/pull/6274/files/cf6ca4fd..dacd7355

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6274&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6274&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6274.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6274/head:pull/6274

PR: https://git.openjdk.java.net/jdk/pull/6274