DevTools: Overrides: do not craft CSS class names.

Crafted names bloat CSS.

BUG=405921
NOTRY=true

Review URL: https://codereview.chromium.org/483303005

git-svn-id: svn://svn.chromium.org/blink/trunk@180789 bbb929c8-8fbe-4397-9dbb-9b2b20218538