DevTools: [Console] refactor ConsoleView and ConsoleGroup classes

This patch cleans up ConsoleView and ConsoleGroup classes to remove some legacy code. No change in behavior.

Review URL: https://codereview.chromium.org/241093002

git-svn-id: svn://svn.chromium.org/blink/trunk@171875 bbb929c8-8fbe-4397-9dbb-9b2b20218538