Reviewed by John.

    Reviewed by John.

        <rdar://problem/4523606> Represent heading elements in AXAttributedStringForTextMarkerRange

        * bridge/mac/WebCoreAXObject.mm:
        (headingLevel):
        (-[WebCoreAXObject headingLevel]):
        (-[WebCoreAXObject isHeading]):
        New. Heading level is per the tag (h1 == 1, h2 == 2, etc.)

        (-[WebCoreAXObject role]):
        (-[WebCoreAXObject roleDescription]):
        Add role and roleDescription for headings.

        (-[WebCoreAXObject value]):
        Value is the headingLevel.

        (AXAttributeStringSetHeadingLevel):
        (AXAttributedStringAppendText):
        Put text's heading level (if applicable) in the attributes.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@15967 268f45cc-cd09-0410-ab3c-d52691b4dbfc