RFR: 8255940: localStorage is null after window.close() [v2]

[Jay Bhaskar]

> Issue: The current implementation of DOMWindow ::localStorage(..) returns null pointer in case of page is being closed. 
> Fix: It should not return nullptr , as per the [w3c web storage spec](https://www.w3.org/TR/2016/REC-webstorage-20160419/) 
> "User agents should expire data from the local storage areas only for security reasons or when requested to do so by the user. User agents should always avoid deleting data while a script that could access that data is running."

Jay Bhaskar has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'openjdk:master' into PRLocalstorage
 - Window.close(), Fix for localstoarge

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/703/files
  - new: https://git.openjdk.java.net/jfx/pull/703/files/12f97feb..73299577

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=703&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=703&range=00-01

  Stats: 416909 lines in 6905 files changed: 234954 ins; 135768 del; 46187 mod
  Patch: https://git.openjdk.java.net/jfx/pull/703.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/703/head:pull/703

PR: https://git.openjdk.java.net/jfx/pull/703