Replace WebFrameLoaderClient static_casts with a function that might return null (WebKit Mac) Spun of from the WK2 version of this bug (https://bugs.webkit.org/show_bug.cgi?id=116253) which was spun off from a targeted fix for a known issue (https://bugs.webkit.org/show_bug.cgi?id=115917)
Only one cast... and this is a dupe of 116324 I guess
*** This bug has been marked as a duplicate of bug 116324 ***