Allow counter-reset/increment: none.

When applying counter-reset/increment with value=none, we did not clear
the CounterDirectives values because the value was not a ValueList.

Fixed by performing the value-clearing before the isValueList-check.

BUG=319812
TEST=automated

Review URL: https://codereview.chromium.org/141763003

git-svn-id: svn://svn.chromium.org/blink/trunk@165753 bbb929c8-8fbe-4397-9dbb-9b2b20218538