[Rev 01] RFR: 8236912: NullPointerException when clicking in WebView with Button 4 or Button 5

[Robert Lichtenberger]

> As documented in JDK-8236912, WebView did not check whether the idMap really contained a mapping for the given button, making it prone to errors, when things are extended (as has happened here).
> 
> The fix consists of two test cases that show the problem in unfixed WebViews and a fix which works analogously to the check whether the given event type is mapped.

The pull request has been updated with 2 additional commits.

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Added commits:
 - 283c5476: 8232524: SynchronizedObservableMap cannot be be protected for copying/iterating
 - 6aecab95: JDK-8232524 fixed.

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/85/files
  - new: https://git.openjdk.java.net/jfx/pull/85/files/542ff60e..283c5476

Webrevs:
 - full: https://webrevs.openjdk.java.net/jfx/85/webrev.01
 - incr: https://webrevs.openjdk.java.net/jfx/85/webrev.00-01

  Stats: 91 lines in 2 files changed: 91 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/85.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/85/head:pull/85

PR: https://git.openjdk.java.net/jfx/pull/85