Disable fullscreen video in OverlayPanels

components/dom_distiller/core/css/distilledpage.css

 /* Copyright 2014 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. */
 
 /* Set the global 'box-sizing' state to 'border-box'.
  * *::after and *::before used to select pseudo-elements not selectable by *. */
 
 *,
 *::after,
 *::before {
@@ skipping 237 matching lines @@
 .dark #closeReaderView {
   border-top: 1px solid #555;
   color: #3adaff;
 }
 
 .sepia #closeReaderView {
   border-top: 1px solid rgb(147, 125, 102);
   color: #55F;
 }
 
+video::-webkit-media-controls-fullscreen-button {
+  display: none;
+}
+
 #closeReaderView {
   /*
   TODO(mdjones): Remove the "display: none;" style when the Reader Mode bar
                  behaves like the toolbar when scrolling.
   */
   display: none;
   flex: 0 0 auto;
   font-family: 'Roboto', sans-serif;
   font-weight: 700;
   line-height: 14px;
@@ skipping 221 matching lines @@
 }
 
 .youtubeIframe {
   height: 100%;
   left: 0px;
   position: absolute;
   top: 0px;
   width: 100%;
 }