Reviewed by David Hyatt and Adele Peterson.

Fix <rdar://problem/7185875>.
        
* page/Frame.cpp:
(WebCore::Frame::setView):
Detach any custom scroll bars from the old view.
        
* page/FrameView.cpp:
(WebCore::FrameView::detachCustomScrollbars):
Simplify the check (and make it work when body is null) by just checking that the scroll bar owner is
not a RenderPart object.

* rendering/RenderObject.cpp:
(WebCore::RenderObject::destroy):
ASSERT that frame() is not null here and also add a null check so that release builds won't crash.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@48070 268f45cc-cd09-0410-ab3c-d52691b4dbfc