Most visited iframe now postMessage to signal the iframing page that the link has been displayed

chrome/browser/resources/local_ntp/most_visited_thumbnail.js

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 /**
  * @fileoverview Rendering for iframed most visited thumbnails.
  */
 
 window.addEventListener('DOMContentLoaded', function() {
   'use strict';
 
   fillMostVisited(document.location, function(params, data) {
     function logEvent(eventName) {
       chrome.embeddedSearch.newTabPage.logEvent(eventName);
     }
     function logImpression(tileIndex, provider) {
       chrome.embeddedSearch.newTabPage.logImpression(tileIndex, provider);
     }
+    function displayLink(link) {
+      document.body.appendChild(link);
+      window.parent.postMessage('linkDisplayed', '*');
+    }
     function showDomainElement() {
-      logEvent(NTP_LOGGING_EVENT_TYPE.NTP_THUMBNAIL_ERROR);
       var link = createMostVisitedLink(
           params, data.url, data.title, undefined, data.ping, data.provider);
       var domain = document.createElement('div');
       domain.textContent = data.domain;
       link.appendChild(domain);
-      document.body.appendChild(link);
+      displayLink(link);
     }
     // Called on intentionally empty tiles for which the visuals are handled
     // externally by the page itself.
     function showEmptyTile() {
-      var link = createMostVisitedLink(
-          params, data.url, data.title, undefined, data.ping, data.provider);
-      document.body.appendChild(link);
-      logEvent(NTP_LOGGING_EVENT_TYPE.NTP_EXTERNAL_TILE);
+      displayLink(createMostVisitedLink(
+          params, data.url, data.title, undefined, data.ping, data.provider));
     }
-    function createAndAppendThumbnail(isVisible) {
+    // Creates and adds an image.
+    function createThumbnail(src) {
       var image = new Image();
       image.onload = function() {
         var shadow = document.createElement('span');
         shadow.classList.add('shadow');
         var link = createMostVisitedLink(
-            params, data.url, data.title, undefined, data.ping, data.provider);
+            params, data.url, data.title, undefined, data.ping,
+            data.provider);
         link.appendChild(shadow);
         link.appendChild(image);
-        // We add 'position: absolute' in anticipation that there could be more
-        // than one thumbnail. This will superpose the elements.
-        link.style.position = 'absolute';
-        document.body.appendChild(link);
+        displayLink(link);
       };
-      if (!isVisible) {
-        image.style.visibility = 'hidden';
-      }
-      return image;
+      image.onerror = function() {
+        logEvent(NTP_LOGGING_EVENT_TYPE.NTP_THUMBNAIL_ERROR);
+        if (data.domain) {
+          logEvent(NTP_LOGGING_EVENT_TYPE.NTP_GRAY_TILE_FALLBACK);
+          showDomainElement();
+        } else {
+          logEvent(NTP_LOGGING_EVENT_TYPE.NTP_EXTERNAL_TILE_FALLBACK);
+          showEmptyTile();
+        }
+      };
+      image.src = src;
     }
+
     // Log an impression if we know the position of the tile.
     if (isFinite(params.pos) && data.provider) {
       logImpression(parseInt(params.pos, 10), data.provider);
     }
 
+    logEvent(NTP_LOGGING_EVENT_TYPE.NTP_TILE);
     if (data.thumbnailUrl) {
-      var image = createAndAppendThumbnail(true);
-      // If a backup thumbnail URL was provided, preload it in case the first
-      // thumbnail errors. The backup thumbnail is always preloaded so that the
-      // server can't gain knowledge on the local thumbnail DB by specifying a
-      // second URL that is only sometimes fetched.
-      if (data.thumbnailUrl2) {
-        var image2 = createAndAppendThumbnail(false);
-        var imageFailed = false;
-        var image2Failed = false;
-        image2.onerror = function() {
-          image2Failed = true;
-          image2.style.visibility = 'hidden';
-          if (imageFailed) {
-            showDomainElement();
-          }
-        };
-        image2.src = data.thumbnailUrl2;
-        // The first thumbnail's onerror function will swap the visibility of
-        // the two thumbnails.
-        image.onerror = function() {
-          logEvent(NTP_LOGGING_EVENT_TYPE.NTP_FALLBACK_THUMBNAIL_USED);
-          imageFailed = true;
-          image.style.visibility = 'hidden';
-          if (image2Failed) {
-            showDomainElement();
-          } else {
-            image2.style.visibility = 'visible';
-          }
-        };
-        logEvent(NTP_LOGGING_EVENT_TYPE.NTP_FALLBACK_THUMBNAIL_REQUESTED);
-      } else {
-        image.onerror = showDomainElement;
-      }
-      image.src = data.thumbnailUrl;
-      logEvent(NTP_LOGGING_EVENT_TYPE.NTP_THUMBNAIL_ATTEMPT);
+      logEvent(NTP_LOGGING_EVENT_TYPE.NTP_THUMBNAIL_TILE);
+      createThumbnail(data.thumbnailUrl);
     } else if (data.domain) {
+      logEvent(NTP_LOGGING_EVENT_TYPE.NTP_GRAY_TILE);
       showDomainElement();
     } else {
+      logEvent(NTP_LOGGING_EVENT_TYPE.NTP_EXTERNAL_TILE);
       showEmptyTile();
     }
   });
 });