[New Tab Page] Local NTP: bound the size of favicon image.

Applied to the old NTP and the fast NTP. Otherwise server-injected favicon
that's bigger than 16x16 will overflow.

BUG=474102

Review URL: https://codereview.chromium.org/1059993002

Cr-Commit-Position: refs/heads/master@{#324045}

chrome/browser/resources/local_ntp/local_ntp.css

@@ -594,6 +594,11 @@ html[dir=rtl] .thumb-ntp .mv-favicon {
   background-size: 16px 16px;
 }
 
+.mv-favicon img {
+  height: 100%;
+  width: 100%;
+}
+
 /* The notification shown when a tile is blacklisted. */
 #mv-notice {
   font-size: 12px;

chrome/browser/resources/local_ntp/most_visited_single.css

@@ -368,6 +368,11 @@ html[dir=rtl] .mv-favicon {
   background-size: 16px 16px;
 }
 
+.mv-favicon img {
+  height: 100%;
+  width: 100%;
+}
+
 .mv-favicon.failed-favicon img {
   display: none;
 }