[GTK] When the WebProcess crashes, a signal should be emitted
https://bugs.webkit.org/show_bug.cgi?id=105180

Reviewed Carlos Garcia Campos.

Emit a "web-process-crashed" signal when the WebProcess crashes. This
is useful, for example, to show an error page in a web browser
like Chrome does.

* UIProcess/API/gtk/WebKitLoaderClient.cpp:
(processDidCrash):
(attachLoaderClientToView):
* UIProcess/API/gtk/WebKitWebContextPrivate.h:
* UIProcess/API/gtk/WebKitWebView.cpp:
(webkit_web_view_class_init):
(webkitWebViewWebProcessCrashed):
* UIProcess/API/gtk/tests/TestWebExtensions.cpp:
(testWebExtensionGetTitle):
(webProcessCrashedCallback):
(testWebKitWebViewProcessCrashed):
(beforeAll):
* UIProcess/API/gtk/tests/WebExtensionTest.cpp:
(methodCallCallback):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148665 268f45cc-cd09-0410-ab3c-d52691b4dbfc