DevTools: Add valid "border-style" property values to CSSMetadata

R=eustas, vsevik
BUG=349998
NOTRY=true

Review URL: https://codereview.chromium.org/194743002

git-svn-id: svn://svn.chromium.org/blink/trunk@168907 bbb929c8-8fbe-4397-9dbb-9b2b20218538