RFR: JDK-8263389 IGV: Zooming changes the point that is currently centered [v2]

[jtfuller111]

> Fixing the zoom issue on IGV. I tested this on Windows and Linux and zooming now works as expected.

jtfuller111 has updated the pull request incrementally with one additional commit since the last revision:

  Zooming now actually keeps the current centered point in the center

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4291/files
  - new: https://git.openjdk.java.net/jdk/pull/4291/files/2bab7337..fcfb23d8

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4291&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4291&range=00-01

  Stats: 19 lines in 1 file changed: 9 ins; 8 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4291.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4291/head:pull/4291

PR: https://git.openjdk.java.net/jdk/pull/4291