Add sample extension to allow/block third-party cookies.

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 333 matching lines @@
       "search_string": "BLANK NEW TAB PAGE  CHROME_URL_OVERRIDES",
       "source_files": [
         "blank.html",
         "manifest.json"
       ],
       "source_hash": "477acf6d15e3fa252e6307e156707538b61c86db",
       "zip_path": "examples\/api\/override\/blank_ntp.zip"
     },
     {
       "api_calls": [
+        "chrome.extension.isAllowedIncognitoAccess"
+      ],
+      "description": "Sample extension which demonstrates how to access a preference.",
+      "features": [
+        "browser_action",
+        "contentSettings",
+        "experimental",
+        "popup"
+      ],
+      "icon": null,
+      "id": "7da105f28e200d42510aff3591dfa5aeb0b82605",
+      "name": "Block\/allow third-party cookies API example extension",
+      "path": "examples\/api\/preferences\/allowThirdPartyCookies\/",
+      "protocols": [],
+      "search_string": "BLOCK\/ALLOW THIRD-PARTY COOKIES API EXAMPLE EXTENSION SAMPLE EXTENSION WHICH DEMONSTRATES HOW TO ACCESS A PREFERENCE. BROWSER_ACTION CONTENTSETTINGS EXPERIMENTAL POPUP CHROME.EXTENSION.ISALLOWEDINCOGNITOACCESS",
+      "source_files": [
+        "manifest.json",
+        "popup.html"
+      ],
+      "source_hash": "0a5411c5d06a2b40b27ce8eef706b0003bb72be8",
+      "zip_path": "examples\/api\/preferences\/allowThirdPartyCookies.zip"
+    },
+    {
+      "api_calls": [
         "chrome.experimental.devtools.audits.addCategory",
         "chrome.extension.onRequest",
         "chrome.extension.sendRequest",
         "chrome.tabs.executeScript",
         "chrome.tabs.sendRequest"
       ],
       "description": "Extends the Developer Tools, adding an audit category that finds broken links on the inspected page.",
       "features": [
         "background_page",
         "devtools_page",
@@ skipping 335 matching lines @@
       "icon": null,
       "id": "0bf0930a32829dfb77170535ecb27adc2de3998a",
       "name": "Enable\/disable referrers API example extension",
       "path": "examples\/api\/preferences\/enableReferrer\/",
       "protocols": [],
       "search_string": "ENABLE\/DISABLE REFERRERS API EXAMPLE EXTENSION SAMPLE EXTENSION WHICH DEMONSTRATES HOW TO ACCESS A PREFERENCE. BROWSER_ACTION CONTENTSETTINGS EXPERIMENTAL POPUP CHROME.EXTENSION.ISALLOWEDINCOGNITOACCESS",
       "source_files": [
         "manifest.json",
         "popup.html"
       ],
-      "source_hash": "2919c196fec8721c240b529b7763c36f7330d986",
+      "source_hash": "3b492332455095ce069e29d9dcff81e429459190",
       "zip_path": "examples\/api\/preferences\/enableReferrer.zip"
     },
     {
       "api_calls": [],
       "description": "A sample extension which uses Google Analytics to track usage.",
       "features": [
         "background_page",
         "browser_action",
         "popup"
       ],
@@ skipping 1135 matching lines @@
       "source_files": [
         "manifest.json",
         "popup.html",
         "sample.css"
       ],
       "source_hash": "c8bfc2b60f25c24dc3c5aaf75dd635c9419df66d",
       "zip_path": "examples\/api\/extension\/isAllowedAccess.zip"
     }
   ]
 }