Reviewed by Kent Tamura.

        https://bugs.webkit.org/show_bug.cgi?id=47645
        Conversion to text test: editing/spelling/spellcheck-attribute.html

        Replaced a pixel test with test-based test using
        LayoutTestController.hasSpellingMarker().

        * editing/spelling/spellcheck-attribute-expected.txt: Added.
        * editing/spelling/spellcheck-attribute.html:
        * platform/chromium-win/editing/spelling/spellcheck-attribute-expected.checksum: Removed.
        * platform/chromium-win/editing/spelling/spellcheck-attribute-expected.png: Removed.
        * platform/chromium-win/editing/spelling/spellcheck-attribute-expected.txt: Removed.
        * platform/chromium/test_expectations.txt:
        * platform/gtk/editing/spelling/spellcheck-attribute-expected.txt: Removed.
        * platform/mac-leopard/editing/spelling/spellcheck-attribute-expected.checksum: Removed.
        * platform/mac-leopard/editing/spelling/spellcheck-attribute-expected.png: Removed.
        * platform/mac/editing/spelling/spellcheck-attribute-expected.checksum: Removed.
        * platform/mac/editing/spelling/spellcheck-attribute-expected.png: Removed.
        * platform/mac/editing/spelling/spellcheck-attribute-expected.txt: Removed.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@70295 268f45cc-cd09-0410-ab3c-d52691b4dbfc