Hide overlay play button if it can't be shown without clipping

third_party/WebKit/Source/core/css/mediaControls.css

 /*
  * Copyright (C) 2009 Apple Inc.  All rights reserved.
  * Copyright (C) 2015 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 105 matching lines @@
 
 video::-webkit-media-controls-overlay-enclosure {
     display: flex;
     position: relative;
     flex-direction: column;
     justify-content: flex-end;
     align-items: center;
     flex: 1 1;
     min-height: 0;
     width: 100%;
-    /* prevent disambiguation zooms with the panel */
+    /* Prevent disambiguation zooms with the panel. If this changes, it must
+     * also be changed in core/html/shadow/MediaControls.cpp. */
     margin-bottom: 10px;
     text-indent: 0;
     box-sizing: border-box;
     overflow: hidden;
 }
 
 video::-webkit-media-controls-overlay-play-button {
     -webkit-appearance: media-overlay-play-button;
     display: flex;
     position: absolute;
@@ skipping 388 matching lines @@
     font-weight: bold;
 }
 
 video::cue(u) {
     text-decoration: underline;
 }
 
 video::cue(i) {
     font-style: italic;
 }