[GTK] Add API to override the default local storage directory
https://bugs.webkit.org/show_bug.cgi?id=138828

Reviewed by Gustavo Noronha Silva.

Source/WebKit2:

Add WebKitWebContext:local-storage-directory construct-only
property. If not provided the default will be used.

* UIProcess/API/gtk/WebKitWebContext.cpp:
(webkitWebContextGetProperty):
(webkitWebContextSetProperty):
(webkitWebContextConstructed):
(webkit_web_context_class_init):

Tools:

Add test to check that the local storage directory is created at
the path given on construction.

* TestWebKitAPI/Tests/WebKit2Gtk/TestWebKitWebContext.cpp:
(testWebContextConfiguration):
(beforeAll):
* TestWebKitAPI/gtk/WebKit2Gtk/TestMain.h:
(Test::Test):
(Test::~Test): Deleted.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@176512 268f45cc-cd09-0410-ab3c-d52691b4dbfc