Add checkup test about Google's Floc

lib/defaults.js

@@ -48,6 +48,7 @@ Default.httpHeaders = function () {
         "X-XSS-Protection": "1; mode=block",
         "X-Content-Type-Options": "nosniff",
         "Access-Control-Allow-Origin": "*",
+        "Permissions-policy":"interest-cohort=()"
     };
 };
 Default.mainPages = function () {

www/checkup/main.js

@@ -365,6 +365,15 @@ define([
         });
     });
 
+    assert(function (cb, msg) {
+        msg.innerText = "Missing HTTP header required to disable Google's Floc.";
+        $.ajax('/?'+ (+new Date()), {
+            complete: function (xhr) {
+                cb(xhr.getResponseHeader('permissions-policy') === 'interest-cohort=()');
+            },
+        });
+    });
+
     assert(function (cb, msg) {
         msg = msg;
         return void cb(true);