Fix debug crash when using CSS Calc in Flexbox order

The parsing for Flexbox property order clamps the just parsed CSS value
to a valid range. This code failed to handle the case when CSS Calc is
used and does not clean up the CSS Calc value correctly.

This patch defers the clamping to style resolving time after the CSS Value
has been resolved to a number and avoids dealing with CSS specific cases.

Updated Flexbox order test to ref test instead of pixel/text test.

BUG=328998

Review URL: https://codereview.chromium.org/142703005

git-svn-id: svn://svn.chromium.org/blink/trunk@165993 bbb929c8-8fbe-4397-9dbb-9b2b20218538