[DevTools] Add test checking that codemirror-based highlighter is loaded.

BUG=none

Review URL: https://codereview.chromium.org/1208423005

git-svn-id: svn://svn.chromium.org/blink/trunk@198277 bbb929c8-8fbe-4397-9dbb-9b2b20218538
3 files changed