Reviewed by Justin.

        - test for http://bugs.webkit.org/show_bug.cgi?id=8928
          <rdar://problem/5045708> REPRODUCIBLE ASSERT: Cannot paste HTML into a
          contenteditable region in an XHTML document (8928)

        * editing/pasteboard/paste-xml-expected.checksum: Added.
        * editing/pasteboard/paste-xml-expected.png: Added.
        * editing/pasteboard/paste-xml-expected.txt: Added.
        * editing/pasteboard/paste-xml.xhtml: Added.

WebCore:

        Reviewed by Justin.

        - fix http://bugs.webkit.org/show_bug.cgi?id=8928
          <rdar://problem/5045708> REPRODUCIBLE ASSERT: Cannot paste HTML into a
          contenteditable region in an XHTML document (8928)

        Test: editing/pasteboard/paste-xml.xhtml

        * editing/markup.cpp: (WebCore::createFragmentFromMarkup): Added a check for 0
        here, since createContextualFragment can return 0 for XML documents that fail
        to parse. In my testing, callers all seem equipped to handle 0.

WebKit:

        Reviewed by Justin.

        - fix http://bugs.webkit.org/show_bug.cgi?id=8928
          <rdar://problem/5045708> REPRODUCIBLE ASSERT: Cannot paste HTML into a
          contenteditable region in an XHTML document (8928)

        * WebView/WebHTMLView.mm:
        (-[WebHTMLView _hasHTMLDocument]): Added.
        (-[WebHTMLView _documentFragmentFromPasteboard:forType:inContext:subresources:]):
        Don't call AppKit's conversion from the DOM to an attributed string if the document
        is not an HTML document, to work around an AppKit limitation (Radar 5052390).



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@20092 268f45cc-cd09-0410-ab3c-d52691b4dbfc