Adding content_security_policy to sample extensions when relevant.

chrome/common/extensions/docs/examples/api/browserAction/make_page_red/manifest.json

 {
   "name": "A browser action with no icon that makes the page red",
   "version": "1.0",
   "background_page": "background.html",
   "permissions": [
     "tabs", "http://*/*"
   ],
   "browser_action": {
       "name": "Make this page red",
       "icons": ["icon.png"]
-  }
-}
+  },
+  "content_security_policy": "default-src 'self'"
+}