RFR: 8255940: localStorage is null after window.close() [v3]

[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 incrementally with three additional commits since the last revision:

 - Change Dir Path and use local Dir and set data before clearing localstorage test
 - Merge branch 'PRLocalstorage' of https://github.com/jaybhaskar/jfx into PRLocalstorage
 - Merge branch 'master' into PRLocalstorage

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/703/files
  - new: https://git.openjdk.java.net/jfx/pull/703/files/73299577..a8647839

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=703&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=703&range=01-02

  Stats: 78 lines in 3 files changed: 68 ins; 1 del; 9 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