Reviewed by Simon Fraser.

        Add a currently-failing test exhibiting the problem in
        https://bugs.webkit.org/show_bug.cgi?id=20674:

        When converting very large or small numbers back to strings, exponential
        notation is used, so a value like 90010000px is returned from
        getComputedStyle() as 9.001e+07px.

        9.001e+07px does not parse, so such a value cannot be round-tripped.

        This is a particular problem with tranformation matrices, which can often
        contain very large or small numbers.

        (Test written by Simon Fraser; I've just made it a committable patch.)

        * fast/css/large-number-round-trip-expected.txt: Added.
        * fast/css/large-number-round-trip.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@49254 268f45cc-cd09-0410-ab3c-d52691b4dbfc