<rdar://problem/5237325> Incorrect AXLeftLineTextMarkerRangeForTextMarker/AXPreviousLineStartTextMarkerForTextMarker for non-editable text
        
        * editing/visible_units.cpp:
        (WebCore::startPositionForLine):
        (WebCore::startOfLine):
        (WebCore::endPositionForLine):
        (WebCore::endOfLine):
        Break down the line routines to allow another try to ask for start/end of line if the returned position is not valid.
        An example would be when lineStart/lineEnd at different line than the input position.
        This can happen if the input position is before the space character at the end of a soft-wrapped non-editable line, 
        specifically a line without webkit-line-break:after-white-space style.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@23608 268f45cc-cd09-0410-ab3c-d52691b4dbfc