RFR: 8270336: [TESTBUG] Fix initialization in NonbranchyTree [v2]

[Leonid Mesnik]

> The nsk.share.gc.NonbranchyTree might call initTree() twice and incorrectly reports branchiness in the case of IllegalArgumentException(...).

Leonid Mesnik has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - fixed typo
 - Merge branch 'master' of https://github.com/openjdk/jdk into 8270336
 - 8270336: [TESTBUG] Fix initialization in NonbranchyTree

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4761/files
  - new: https://git.openjdk.java.net/jdk/pull/4761/files/4782c3f1..ea166692

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4761&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4761&range=00-01

  Stats: 5276 lines in 207 files changed: 3289 ins; 1015 del; 972 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4761.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4761/head:pull/4761

PR: https://git.openjdk.java.net/jdk/pull/4761