DevTools: [Styles] Make sure WebInspector.Color.Nicknames keys are lowercase

R=pfeldman, vsevik
BUG=307482
NOTRY=true

Review URL: https://codereview.chromium.org/27322002

git-svn-id: svn://svn.chromium.org/blink/trunk@160193 bbb929c8-8fbe-4397-9dbb-9b2b20218538