DevTools: Add "inset" and "none" values for "box-shadow" property in CSSMetadata

R=aandrey, eustas, vsevik
BUG=332355

Review URL: https://codereview.chromium.org/131423002

git-svn-id: svn://svn.chromium.org/blink/trunk@164860 bbb929c8-8fbe-4397-9dbb-9b2b20218538