Reviewed by Ojan Vafai.

        new-run-webkit-tests: clean up code for test_types, test_failures

        Add a bunch of unit tests for webkitpy.layout_tests.test_types and
        webkitpy.layout_tests.layout_package.test_failures, and remove
        some dead code and otherwise clean up things.

        https://bugs.webkit.org/show_bug.cgi?id=44559

        * Scripts/webkitpy/layout_tests/layout_package/test_failures.py:
        * Scripts/webkitpy/layout_tests/layout_package/test_failures_unittest.py: Added.
        * Scripts/webkitpy/layout_tests/rebaseline_chromium_webkit_tests.py:
        * Scripts/webkitpy/layout_tests/test_types/image_diff.py:
        * Scripts/webkitpy/layout_tests/test_types/test_type_base.py:
        * Scripts/webkitpy/layout_tests/test_types/test_type_base_unittest.py: Added.
        * Scripts/webkitpy/layout_tests/test_types/text_diff.py:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@65953 268f45cc-cd09-0410-ab3c-d52691b4dbfc