RFR: 6669: FlameGraphView tree calculation should (probably) be interruptable

[Miroslav Wengner]

fix to bug: https://bugs.openjdk.java.net/browse/JMC-6669

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Commit messages:
 - 6669: spotless needs
 - 6669: model calculation cancelation

Changes: https://git.openjdk.java.net/jmc/pull/135/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=135&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6669
  Stats: 25 lines in 1 file changed: 12 ins; 2 del; 11 mod
  Patch: https://git.openjdk.java.net/jmc/pull/135.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/135/head:pull/135

PR: https://git.openjdk.java.net/jmc/pull/135