DevTools: make extension server a part of core, panels' code should depend on it.

drive-by removal of random selection-related undocumented extensions api capabilities.

BUG=424951

Review URL: https://codereview.chromium.org/667623002

git-svn-id: svn://svn.chromium.org/blink/trunk@183969 bbb929c8-8fbe-4397-9dbb-9b2b20218538