Reviewed by Eric Seidel.

        new-run-webkit-tests: turn off threading on the Chromium Mac port until
        we can stabilize the port more and figure out why it is hanging so
        frequently.

        https://bugs.webkit.org/show_bug.cgi?id=38553

        * Scripts/webkitpy/layout_tests/port/chromium_mac.py:
          - override default_child_processes() and log a warning
        * Scripts/webkitpy/layout_tests/run_webkit_tests.py:
          - fix a typo that caused us to print a method object instead of the
            value the method object returns in the case where there is only
            one child process.
        * Scripts/webkitpy/layout_tests/run_webkit_tests_unittest.py:
          - Add unit tests for the output of run_webkit_tests - in this case,
            the handling of --child-processes and --print config

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@58789 268f45cc-cd09-0410-ab3c-d52691b4dbfc