[New Tab Page] Remove title iframe 1px dead zone.

Material Design tile titles are 15px high, but on some (if not all)
platforms the natural height of title content is 14px high. This creates
a click "dead zone" on the tile. This CL forces content height to be
100% to remove the dead zone.

BUG=459301

Review URL: https://codereview.chromium.org/938473002

Cr-Commit-Position: refs/heads/master@{#317633}

chrome/browser/resources/local_ntp/most_visited_title.css

 /* 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. */
+html {
+  height: 100%;
+}
+
 body {
+  height: 100%;
   width: 100%;
 }
 
 a {
+  height: 100%;
   overflow: hidden;
   text-align: center;  /* Can be overridden in JS. */
   text-overflow: ellipsis; /* Can be overridden in JS. */