RFR: 8276553: ListView scrollTo() is broken after fix for JDK-8089589 [v2]

[Johan Vos]

> After (re)setting the number of elements, make sure to do at least some estimation of the total size.
> Added a testcase for this scenario.

Johan Vos has updated the pull request incrementally with one additional commit since the last revision:

  Move functionality in the setCellCount() to the invalidated block.
  Some hard numbers used in tests (counters for evaluations) were changed because of this.
  Instead of relying on hard values, I modified the failing was into relative ones.

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/683/files
  - new: https://git.openjdk.java.net/jfx/pull/683/files/1a0ce697..b3fe2756

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=683&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=683&range=00-01

  Stats: 18 lines in 4 files changed: 6 ins; 4 del; 8 mod
  Patch: https://git.openjdk.java.net/jfx/pull/683.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/683/head:pull/683

PR: https://git.openjdk.java.net/jfx/pull/683