RFR: JDK-8299977 : Update WebKit to 615.1 [v3]

[Hima Bindu Meda]

> Update JavaFX WebKit to GTK WebKit 2.38 (615.1).
> 
> Verified the updated version build, sanity tests and stability.
> This does not cause any issues except one unit test failure.
> Also, there are some artifacts observed while playing youtube
> 
> The above issues are recorded and ignored using below bugs:
> [JDK-8300954](https://bugs.openjdk.org/browse/JDK-8300954)
> [JDK-8301022](https://bugs.openjdk.org/browse/JDK-8301022)

Hima Bindu Meda has updated the pull request incrementally with one additional commit since the last revision:

  Remove the log added for testing purpose

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1011/files
  - new: https://git.openjdk.org/jfx/pull/1011/files/66237d46..a804a6ed

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1011&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1011&range=01-02

  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1011.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/1011/head:pull/1011

PR: https://git.openjdk.org/jfx/pull/1011