Adds a new UMA histogram to measure the NTP load time since navigation

chrome/browser/resources/local_ntp/most_visited_thumbnail.js

Index: chrome/browser/resources/local_ntp/most_visited_thumbnail.js
diff --git a/chrome/browser/resources/local_ntp/most_visited_thumbnail.js b/chrome/browser/resources/local_ntp/most_visited_thumbnail.js
index 2c3e770702b85e8ed2cd2d105182cce47b83cde9..70ee4a7cbae6c4535aaad40d8ade4e3256c023d5 100644
--- a/chrome/browser/resources/local_ntp/most_visited_thumbnail.js
+++ b/chrome/browser/resources/local_ntp/most_visited_thumbnail.js
@@ -51,6 +51,7 @@ window.addEventListener('DOMContentLoaded', function() {
         link.appendChild(blocker);
         link.appendChild(image);
         displayLink(link);
+        logEvent(NTP_LOGGING_EVENT_TYPE.NTP_TILE_LOADED);
       };
       image.onerror = function() {
         // If no external thumbnail fallback (etfb), and have domain.
@@ -62,6 +63,7 @@ window.addEventListener('DOMContentLoaded', function() {
           logEvent(NTP_LOGGING_EVENT_TYPE.NTP_EXTERNAL_TILE_FALLBACK);
         }
         logEvent(NTP_LOGGING_EVENT_TYPE.NTP_THUMBNAIL_ERROR);
+        logEvent(NTP_LOGGING_EVENT_TYPE.NTP_TILE_LOADED);
       };
       image.src = src;
     }