DevTools: Introduce ExtendableTabbedPaneController that allows to fill tabbed pane using extensions.

Drive-by: Get rid of ViewFactories, pass view constructors instead.

R=pfeldman@chromium.org, pfeldman

Review URL: https://codereview.chromium.org/200293003

git-svn-id: svn://svn.chromium.org/blink/trunk@169327 bbb929c8-8fbe-4397-9dbb-9b2b20218538