DevTools: Implement a draft of WebInspector.Context

R=pfeldman, vsevik
NOTRY=true

Review URL: https://codereview.chromium.org/233203002

git-svn-id: svn://svn.chromium.org/blink/trunk@171274 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: better address console self-xss.

BUG=345205
R=vsevik@chromium.org

Review URL: https://codereview.chromium.org/232023005

git-svn-id: svn://svn.chromium.org/blink/trunk@171275 bbb929c8-8fbe-4397-9dbb-9b2b20218538