RFR: JDK-8289182: NMT: MemTracker::baseline should return void [v2]

[Thomas Stuefe]

> Small cleanup.
> 
> Since MemTracker::baseline() only returns true, it can revert to void, and error handling can be removed from all callers.

Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains one commit:

  let MemTracker::baseline return void

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Changes: https://git.openjdk.org/jdk/pull/9288/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9288&range=01
  Stats: 47 lines in 8 files changed: 0 ins; 11 del; 36 mod
  Patch: https://git.openjdk.org/jdk/pull/9288.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9288/head:pull/9288

PR: https://git.openjdk.org/jdk/pull/9288