[Local NTP] Add an integration test for the most visited iframe

chrome/test/data/local_ntp_browsertest.js

Index: chrome/test/data/local_ntp_browsertest.js
diff --git a/chrome/test/data/local_ntp_browsertest.js b/chrome/test/data/local_ntp_browsertest.js
index bb33e34723b31565c1c0e50d3d98153131c9c2c1..f16fc95f3ebf68c612fd34b1f3241e30c2300c1f 100644
--- a/chrome/test/data/local_ntp_browsertest.js
+++ b/chrome/test/data/local_ntp_browsertest.js
@@ -139,7 +139,18 @@ function testMostVisitedContents() {
 // Advanced tests are controlled from the native side. The helpers here are
 // called from native code to set up the page and to check results.
 
-function setupAdvancedTest() {
+function handlePostMessage(event) {
+  if (event.data.cmd == 'loaded') {
+    domAutomationController.setAutomationId(0);
+    domAutomationController.send('loaded');
+  }
+}
+
+function setupAdvancedTest(opt_waitForIframeLoaded) {
+  if (opt_waitForIframeLoaded) {
+    window.addEventListener('message', handlePostMessage);
+  }
+
   setUp();
   initLocalNTP(/*isGooglePage=*/true);