RFR: 8272808: Update constant collections to use the new immutable collections - leftovers [v3]

[Nir Lisker]

> Replacements of more immutable collections.
> 
> One thing I found was that the field `idMap` in `com.sun.java.scene.web.WebViewHelper.WebView` seems unused. I can remove it if that's indeed the case.

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

  Removed unused field

-------------

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/627/files
  - new: https://git.openjdk.java.net/jfx/pull/627/files/79606579..fc72e5dd

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=627&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=627&range=01-02

  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/627.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/627/head:pull/627

PR: https://git.openjdk.java.net/jfx/pull/627