DevTools: [Styles] Unprefix the "transform" property

Both prefixed and unprefixed property variants in value prompts shall be considered in property weight computation.

R=eustas, vsevik
BUG=366456

Review URL: https://codereview.chromium.org/251503002

git-svn-id: svn://svn.chromium.org/blink/trunk@172476 bbb929c8-8fbe-4397-9dbb-9b2b20218538