DevTools: Introduce "codemirror" module, use DI instead of direct CodeMirror dependencies

R=pfeldman@chromium.org, pfeldman

Review URL: https://codereview.chromium.org/145353006

git-svn-id: svn://svn.chromium.org/blink/trunk@166208 bbb929c8-8fbe-4397-9dbb-9b2b20218538