Fix API test introduced in r239339 on iOS.

Fix API test introduced in r239339 on iOS.
https://bugs.webkit.org/show_bug.cgi?id=192675

* TestWebKitAPI/Tests/WebKitCocoa/SafeBrowsing.mm:
(TEST):
The iOS implementation of the safe browsing warning is a little different.
It does some element creation when it is added to the window so it knows how big it is.
To test these elements, we need to simulate adding it to the window.
A similar technique is done in other iOS API tests, such as SafeBrowsing.ShowWarningSPI.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@239356 268f45cc-cd09-0410-ab3c-d52691b4dbfc