Web Inspector: [Settings] Use registry to track settings objects.
https://bugs.webkit.org/show_bug.cgi?id=113008

Reviewed by Pavel Feldman.

Currently .createSetting creates new instance any time it is invoked.
When one instance saves value, the other instance do not know about it.

To resolve this issue we can use registry to make .createSetting return
same object for specific key.

* inspector/front-end/Settings.js:
(WebInspector.Settings.prototype.createSetting): Use registry.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146745 268f45cc-cd09-0410-ab3c-d52691b4dbfc