RFR: 8238526: Cherry pick GTK WebKit 2.26.3 changes

[Guru Hb]

Fix contains https://webkitgtk.org/2020/01/22/webkitgtk2.26.3-released.html

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Commits:
 - 025373db: 8238526: Cherry pick GTK WebKit 2.26.3 changes

Changes: https://git.openjdk.java.net/jfx/pull/107/files
 Webrev: https://webrevs.openjdk.java.net/jfx/107/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8238526
  Stats: 123 lines in 19 files changed: 39 ins; 59 del; 25 mod
  Patch: https://git.openjdk.java.net/jfx/pull/107.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/107/head:pull/107

PR: https://git.openjdk.java.net/jfx/pull/107