[CSSGridLayout] grid-auto-columns-rows-update.html not working

Modifying the expected results of the test mentioned in the title was not
causing test failures. This means that the test was not testing anything as it
was always working no matter the values of the expected results.

The reason why it was not working is r173426. That revision modified the way
checkLayout compares the expected and the actual results. It isn't using
parseInt() anymore so in the end we were comparing things like "20px vs 20" or
"10px vs 10". The result of that comparison is NaN. As NaN is not >= 1 then the
result of the comparison was considered valid by mistake.

The fix is to remove the 'px' suffix from the expected result.

Review URL: https://codereview.chromium.org/531063002

git-svn-id: svn://svn.chromium.org/blink/trunk@181324 bbb929c8-8fbe-4397-9dbb-9b2b20218538