Use content extensions in MiniBrowser.

Use content extensions in MiniBrowser.
https://bugs.webkit.org/show_bug.cgi?id=143446

Patch by Sam Weinig <sam@webkit.org> on 2015-04-06
Reviewed by Alex Christensen.

* MiniBrowser/MiniBrowser.xcodeproj/project.pbxproj:
* MiniBrowser/mac/AppDelegate.h:
* MiniBrowser/mac/AppDelegate.m:
(-[BrowserAppDelegate init]):
(-[BrowserAppDelegate showExtensionsManager:]):
(-[BrowserAppDelegate userContentContoller]):
* MiniBrowser/mac/ExtensionManagerWindowController.h: Added.
* MiniBrowser/mac/ExtensionManagerWindowController.m: Added.
(-[ExtensionManagerWindowController init]):
(-[ExtensionManagerWindowController windowDidLoad]):
(-[ExtensionManagerWindowController add:]):
(-[ExtensionManagerWindowController remove:]):
* MiniBrowser/mac/ExtensionManagerWindowController.xib: Added.
* MiniBrowser/mac/MainMenu.xib:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@182476 268f45cc-cd09-0410-ab3c-d52691b4dbfc