RFR: 6542: Improve calls to render in the flame view

[Miroslav Wengner]

the Flameview shift fix during a fast scrolling over the selections: https://bugs.openjdk.java.net/browse/JMC-6542

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Commit messages:
 - 6542: comments model calculation cancelation
 - 6542: cleanup
 - 6542: correction flameview display,  model calculation separation

Changes: https://git.openjdk.java.net/jmc/pull/133/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=133&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6542
  Stats: 92 lines in 1 file changed: 45 ins; 25 del; 22 mod
  Patch: https://git.openjdk.java.net/jmc/pull/133.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/133/head:pull/133

PR: https://git.openjdk.java.net/jmc/pull/133