Bug 1256251 - Update browser.cookies.onChanged to match Chrome's behaviour when overwriting a cookie. r=kmag

MozReview-Commit-ID: 5AGXbfkOd9R

--HG--
extra : transplant_source : %02%5D%D0%98%99x%3E%A5%ED%E8%87%3A%82%05%CAe%3B%7F%CB%C7

toolkit/components/extensions/ext-cookies.js

@@ -331,7 +331,8 @@ extensions.registerSchemaAPI("cookies", "cookies", (extension, context) => {
               notify(false, subject, "explicit");
               break;
             case "changed":
-              notify(false, subject, "overwrite");
+              notify(true, subject, "overwrite");
+              notify(false, subject, "explicit");
               break;
             case "batch-deleted":
               subject.QueryInterface(Ci.nsIArray);

toolkit/components/extensions/test/mochitest/test_ext_cookies_permissions.html

@@ -73,7 +73,7 @@ function* testCookies(options) {
           changed.splice(evicted, 1);
         }
 
-        browser.test.assertEq("x:explicit,x:overwrite,x:explicit,foo:overwrite,bar:explicit,deleted:explicit",
+        browser.test.assertEq("x:explicit,x:overwrite,x:explicit,x:explicit,foo:overwrite,foo:explicit,bar:explicit,deleted:explicit",
                               changed.join(","), "expected changes");
       } else {
         browser.test.assertEq("", changed.join(","), "expected no changes");