[jfx20u] Integrated: 8303217: Webview loaded webpage is not showing play, volume related buttons for embeded Audio/Video elements

[Kevin Rushforth]

Clean backport to `jfx20u`. Tested in connection with all other WebKit backports in `jfx-20.0.1` branch.

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Commit messages:
 - 8303217: Webview loaded webpage is not showing play, volume related buttons for embeded Audio/Video elements

Changes: https://git.openjdk.org/jfx20u/pull/8/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx20u&pr=8&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303217
  Stats: 400 lines in 18 files changed: 396 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/jfx20u/pull/8.diff
  Fetch: git fetch https://git.openjdk.org/jfx20u pull/8/head:pull/8

PR: https://git.openjdk.org/jfx20u/pull/8