Fix favicon repeat on Mac

Bug: 1099917
Change-Id: I26318b0c4fc054f9627a5208f4dfcbb5e5608486
Reviewed-on: https://chrome-internal-review.googlesource.com/c/chrome/browser/resources/tab_search/+/3273923Reviewed-by: Tom Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819603}

chrome/browser/resources/tab_search_merge/tab_search_item.html

@@ -18,6 +18,8 @@
   }
 
   .favicon {
+    background-repeat: no-repeat;
+    background-size: var(--mwb-icon-size);
     flex-shrink: 0;
     height: var(--mwb-icon-size);
     margin-inline-end: var(--mwb-list-item-horizontal-margin);