[CSS Shapes] polygon y-value calc() args serialize incorrectly

The code hit ASSERT(isCalculation(value)) in CSSParser::createPrimitiveNumbericValue, because
CSSParser::validUnit had been called on both coordinates, which set the value for m_parsedCalculation,
but only one of the coordinates was calculation value. I reordered calling valudUnit and
createPrimitiveNumbericValue to be called in the correct order on the coordinates.

I added the new test case to parsing-test-utils.js.

This is a merge of http://trac.webkit.org/changeset/166813 by Zoltan Horvath <zoltan@webkit.org>.

BUG=350182

Review URL: https://codereview.chromium.org/225183016

git-svn-id: svn://svn.chromium.org/blink/trunk@171689 bbb929c8-8fbe-4397-9dbb-9b2b20218538