Reviewed by Maciej.

    Reviewed by Maciej.

        <rdar://problem/4407336> Some non-text elements return AXTextMarkerRangeForUIElement with equal start and end marker

        * bridge/mac/WebCoreAXObject.mm:
        (-[WebCoreAXObject textMarkerRange]):
        Use 0 and maxDeepOffset(), instead of caretMinOffset() and caretMaxRenderedOffset().
        Check for VisiblePositions being equal.  If so, adjust end one to its next().
        That happens with, e.g., buttons.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@15965 268f45cc-cd09-0410-ab3c-d52691b4dbfc