Reviewed by darin
        
        <rdar://problem/5168598> Crash when deleting a link inside an input field

        * editing/deleting/5168598-expected.checksum: Added.
        * editing/deleting/5168598-expected.png: Added.
        * editing/deleting/5168598-expected.txt: Added.
        * editing/deleting/5168598.html: Added.

WebCore:

        Reviewed by darin

        <rdar://problem/5168598> 
        Crash when deleting a link inside an input field
        
        Deletion code tries to update one of its positions to keep 
        it valid and nullifies it.  Later in mergeParagraphs we try 
        to find out if it's valid by checking to see if it's still in 
        the document and crash.
        
        The fix is just to not bother keeping the position, 
        m_upstreamStart, valid, since after the point in the code 
        under examination, it doesn't need to be valid anymore.  
        Besides, code to update DeleteSelectionCommand's positions 
        should go in the functions that handle the content removal 
        that might invalid them (there are already FIXMEs about this).
        
        Also, users shouldn't be able to insert links (or any rich content)
        into plaintext-only regions like text fields, even if those
        text fields are inside richly editable regions.  This is a 
        separate bug and is filed as 5171552.

        * editing/DeleteSelectionCommand.cpp:
        (WebCore::DeleteSelectionCommand::handleGeneralDelete): Don't
        bother updating m_upstreamStart.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@21195 268f45cc-cd09-0410-ab3c-d52691b4dbfc