Improving `content_security_policy` documentation.

chrome/common/extensions/docs/samples.json

 {
   "api": {
     "chrome.bookmarks.create": "bookmarks.html#method-create",
     "chrome.bookmarks.export": "bookmarks.html#method-export",
     "chrome.bookmarks.get": "bookmarks.html#method-get",
     "chrome.bookmarks.getChildren": "bookmarks.html#method-getChildren",
     "chrome.bookmarks.getRecent": "bookmarks.html#method-getRecent",
     "chrome.bookmarks.getSubTree": "bookmarks.html#method-getSubTree",
     "chrome.bookmarks.getTree": "bookmarks.html#method-getTree",
     "chrome.bookmarks.import": "bookmarks.html#method-import",
@@ skipping 847 matching lines @@
         "options.html"
       ],
       "source_hash": "06c9cd22fddedb3a0f10e1884270eea652622267",
       "zip_path": "examples\/extensions\/email_this_page.zip"
     },
     {
       "api_calls": [],
       "crx_path": null,
       "description": "A sample extension which uses Google Analytics to track usage.",
       "features": [
-        "background_page",
         "browser_action"
       ],
       "icon": "analytics-extension-icon-128.png",
       "id": "763a08e9b06595d785568a8d392b95a2f3700258",
       "name": "Event Tracking with Google Analytics",
       "packaged_app": false,
       "path": "examples\/tutorials\/analytics\/",
       "protocols": [],
-      "search_string": "EVENT TRACKING WITH GOOGLE ANALYTICS A SAMPLE EXTENSION WHICH USES GOOGLE ANALYTICS TO TRACK USAGE. BACKGROUND_PAGE BROWSER_ACTION",
+      "search_string": "EVENT TRACKING WITH GOOGLE ANALYTICS A SAMPLE EXTENSION WHICH USES GOOGLE ANALYTICS TO TRACK USAGE. BROWSER_ACTION",
       "source_files": [
-        "analytics.js",
         "manifest.json",
-        "popup.html"
+        "popup.html",
+        "popup.js"
       ],
-      "source_hash": "48c84c58d7b3673be329cedb1b1351a6a23958ff",
+      "source_hash": "c8d53a870ce15eff468b8fceb0ce454a8dc1e566",
       "zip_path": "examples\/tutorials\/analytics.zip"
     },
     {
       "api_calls": [
         "chrome.devtools.network.getHAR",
         "chrome.devtools.network.onRequestFinished",
         "chrome.extension.onRequest",
         "chrome.extension.sendRequest",
         "chrome.tabs.executeScript"
       ],
@@ skipping 1567 matching lines @@
         "manifest.json",
         "popup.html",
         "popup.js",
         "sample.css"
       ],
       "source_hash": "8e51dc3a9577065d22ce92f3c838edc5ceaf4e65",
       "zip_path": "examples\/api\/extension\/isAllowedAccess.zip"
     }
   ]
 }