[WK2] Text notifications should have an iconURL

[WK2] Text notifications should have an iconURL
https://bugs.webkit.org/show_bug.cgi?id=77968

Reviewed by Simon Hausmann.

Per http://www.w3.org/TR/notifications simple text notifications should have an iconURL.
Add an iconURL to WebNotification and add a public API to access it.

* UIProcess/API/C/WKNotification.cpp:
(WKNotificationCopyiconURL):
* UIProcess/API/C/WKNotification.h:
* UIProcess/Notifications/WebNotification.cpp:
(WebKit::WebNotification::WebNotification):
* UIProcess/Notifications/WebNotification.h:
(WebKit::WebNotification::create):
(WebKit::WebNotification::iconURL):
(WebNotification):
* UIProcess/Notifications/WebNotificationManagerProxy.cpp:
(WebKit::WebNotificationManagerProxy::show):
* UIProcess/Notifications/WebNotificationManagerProxy.h:
(WebNotificationManagerProxy):
* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::showNotification):
* UIProcess/WebPageProxy.h:
(WebPageProxy):
* UIProcess/WebPageProxy.messages.in:
* WebProcess/Notifications/WebNotificationManager.cpp:
(WebKit::WebNotificationManager::show):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@107068 268f45cc-cd09-0410-ab3c-d52691b4dbfc