Move contentSettings extension API out of experimental

chrome/test/data/extensions/api_test/content_settings/getresourceidentifiers/test.html

 <script>
 // Content settings API test
 // Run with browser_tests
 //     --gtest_filter=ExtensionApiTest.ContentSettingsGetResourceIdentifiers
 
 Object.prototype.forEach = function(f) {
   for (key in this) {
     if (this.hasOwnProperty(key))
       f(key, this[key]);
   }
 }
 
-var cs = chrome.experimental.contentSettings;
+var cs = chrome.contentSettings;
 chrome.test.runTests([
   function getResourceIdentifiers() {
     var contentTypes = {
       "cookies": undefined,
       "images": undefined,
       "javascript": undefined,
       "plugins": [
         {
           "description": "Foo",
           "id": "foo",
         },
         {
           "description": "Bar Plugin",
           "id": "bar.plugin",
         },
       ],
       "popups": undefined,
       "notifications": undefined
     };
     contentTypes.forEach(function(type, identifiers) {
       cs[type].getResourceIdentifiers(chrome.test.callbackPass(function(value) {
         chrome.test.assertEq(identifiers, value);
       }));
     });
   },
 ]);
 </script>