All of MiniBrowser's WKWebViews should share a configuration

All of MiniBrowser's WKWebViews should share a configuration
https://bugs.webkit.org/show_bug.cgi?id=134017

Reviewed by Anders Carlsson.

* MiniBrowser/mac/WK2BrowserWindowController.m:
(-[WK2BrowserWindowController awakeFromNib]):
Share a single WKWebViewConfiguration between all of MiniBrowser's views.
This means that they'll share things like preferences, visited links, etc.
It also means that we'll properly share processes once we hit the process limit.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@170122 268f45cc-cd09-0410-ab3c-d52691b4dbfc