[CSS Shapes] CSS parser accepts trailing position arguments

Do not accept the basic shape if there are any trailing arguments in the function list.

BUG=350565

Review URL: https://codereview.chromium.org/191553003

git-svn-id: svn://svn.chromium.org/blink/trunk@168933 bbb929c8-8fbe-4397-9dbb-9b2b20218538