DevTools: Move content scripts to a separate project.

This patch makes a separate project type for content scripts there by removing the isContentScript flag from uiSourceCode.

Drive-by: introduce a setting to set up whether content scripts should be shown in navigator
and searched by advanced search.

R=pfeldman

Review URL: https://codereview.chromium.org/236313016

git-svn-id: svn://svn.chromium.org/blink/trunk@172043 bbb929c8-8fbe-4397-9dbb-9b2b20218538