[GTK] Use WebKitWebContext in WebKitWebView

[GTK] Use WebKitWebContext in WebKitWebView
https://bugs.webkit.org/show_bug.cgi?id=67990

Reviewed by Martin Robinson.

Use webkit_web_context_get_default() instead of
WKContextGetSharedProcessContext() and add API to create a view
with a given web context and to return the current context
associated to the view.

* GNUmakefile.am: Add new files to compilation.
* UIProcess/API/gtk/WebKitPrivate.h: Added.
* UIProcess/API/gtk/WebKitWebContext.cpp:
(webkitWebContextGetWKContext): Private API to get the WKContext
wrapped by the WebKitWebContext.
* UIProcess/API/gtk/WebKitWebContextPrivate.h: Added.
* UIProcess/API/gtk/WebKitWebView.cpp:
(webkitWebViewConstructed): Create the webpage using the web
context of the view.
(webkitWebViewSetProperty):
(webkitWebViewGetProperty):
(webkit_web_view_init):
(webkit_web_view_class_init):
(webkit_web_view_new): Create a new view with the default context.
(webkit_web_view_new_with_context): Create a new view with the
given context.
(webkit_web_view_get_context): Return the context.
* UIProcess/API/gtk/WebKitWebView.h:
* UIProcess/API/gtk/tests/testwebview.c: Added.
(testWebViewDefaultContext):
(main):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@96136 268f45cc-cd09-0410-ab3c-d52691b4dbfc