[Local NTP] block image-related context menu items for thumbnails; CSS fixes.

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 105f85ab1dce17a17f69cc04e9eb7d7bfbd8d118..e18efd604566c2d79d5d7f82e1607765cedcc1bd 100644
--- a/chrome/browser/resources/local_ntp/most_visited_thumbnail.js
+++ b/chrome/browser/resources/local_ntp/most_visited_thumbnail.js
@@ -45,6 +45,10 @@ window.addEventListener('DOMContentLoaded', function() {
         var link = createMostVisitedLink(
             params, data.url, data.title, undefined, data.direction,
             data.provider);
+        // Use blocker to prevent context menu from showing image-related items.
+        var blocker = document.createElement('span');
+        blocker.className = 'blocker';
+        link.appendChild(blocker);
         link.appendChild(image);
         displayLink(link);
       };